- Email: [email protected]
Conversion of carp roe mass to caviar substitutes: Stabilization with oregano extract
LWT - Food Science and Technology 108 (2019) 446–455
Contents lists available at ScienceDirect
LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt
Conversion of carp roe mass to caviar substitutes: Stabilization with oregano extract
T
P.K. Binsia,∗, Natasha Nayaka, P.C. Sarkarb,1, Upali Sahub,1, K.V. Lalithaa, George Ninana, C.N. Ravishankara a b
ICAR- Central Institute of Fisheries Technology, Matsyapuri, Willingdon Island, Cochin, 682 029, India ICAR - Indian Institute of Natural Resins and Gums, Namkum, Ranchi, 834 010, India
ARTICLE INFO
ABSTRACT
Keywords: Caviar substitutes Carp roe Oregano extract Alginate Chilled storage
Fish roe is a nutritionally rich source of polyunsaturated fatty acids, essential amino acids and several vitamins. However, its utilization is currently limited to caviars from a few fish species, as most of others form a jelly mass on cooking. In the present study, freeze dried carp roe mass was converted to caviar substitutes by reconstituting with sodium alginate. Further, oregano extract was added at different concentrations to the mixture as antioxidant and antimicrobial agent before casting. Scanning electron microscopic image revealed a honey-comb like structure for the freeze dried caviar samples, congenial for the retention of oregano extract for an extended period. DSC profile of caviar substitutes confirmed the stability and availability of caviar constituents at boiling temperature. Further, the biochemical, microbial and textural characteristics of caviar substitutes during storage at 4 °C indicated lower bacterial count and minimum generation of lipid oxidation products in caviar substitutes containing 0.5% oregano extract.
1. Introduction Fish roe is a nutritionally rich component, which are usually discarded as waste during processing operations. The contribution of roe to the whole body weight of carps may be as high as 30% during spawning seasons. The superior nutritional value of fish roe arises from its unique amino acid profile coupled with the high content of polyunsaturated fatty acids such as EPA and DHA, and vitamin B. The major amino acids are glutamic acid, leucine, proline, lysine and aspartic acid, and is poor in methionine, cysteine, tyrosine and tryptophan (Binsi et al., 2016a). However, these compositional features are also responsible for the fast spoilage of fish roe during storage due to microbial and oxidative changes. Caviar is a high value delicacy made from fish roe by treating with food grade salt. The term ‘caviar’ is conventionally reserved to certain varieties of fish roe, popularly from the members of Acipenseridae Family (Acipenser sp.), sturgeon fish. Over time, the overexploitation of sturgeons for caviar processing has led to the fast depletion of sturgeon population. Hence, there is high demand for simulated/imitation caviar alternatives prepared using roe from easily available fish species including farmed fishes. Researchers are continuously putting effort in
this line for alternative forms such as simulated caviar, caviar substitutes, reconstituted caviar etc. Eventhough, these alternative forms resemble caviar in appearance and sensory perception, they may contain components other than fish roe, such as gelling and flavouring agents. Alginates are commonly employed gelling agents, which are primarily isolated from brown algae. Previously, the preparation of caviar substitutes by dripping the homogenate of fish roe and alginate into a divalent solution was reported by a couple of researchers (Daemi & Barikani, 2012; Klokk & Melvik, 2002). However, the shelf life of such preparations are limited to a few days under chilled condition. The high PUFA content of fish roe makes it highly susceptible for auto-oxidation and the high free amino acid content enhances microbial degradation. Generally, caviars are considered as cured products containing high proportion of salt, which primarily acts as the preservatory agent. However, due to health reasons alternative preservation strategies are in demand. Plant extracts are rich in polyphenols and several other bioactive substances, which serve as potent antioxidant and antibacterial agents. The protective effect of oregano extract and a few other plant extracts as antioxidant, antibacterial as well as texture modifying agent was observed in our earlier studies (Binsi et al., 2016;
Corresponding author. E-mail address: [email protected] (P.K. Binsi). 1 Present address: National Institute of Research on Jute and allied fibre technology ICAR-NIRJAFT, 12 Regent Park, Tollygunge, Kolkata – 700040. ∗
https://doi.org/10.1016/j.lwt.2019.03.001 Received 23 November 2018; Received in revised form 27 February 2019; Accepted 1 March 2019 Available online 13 March 2019 0023-6438/ © 2019 Elsevier Ltd. All rights reserved.
LWT - Food Science and Technology 108 (2019) 446–455
P.K. Binsi, et al.
Binsi et al., 2017a; Binsi, Ninan, & Ravishankar, 2017b; Viji, Binsi, Visnuvinayagam, Ravishankar, Venkateshwarlu, & Gopal., 2015). Hence, in the present study oregano extract was added at various levels to the roe-alginate mixture prior to casting, and the antioxidant, antibacterial, and texture modifying effects was evaluated. Based on our previous observations, the hypothesis of the present study was that, the inferior texture and the limited shelf life of fish roe based products such as caviar substitute may be improved by incorporating polyphenol rich oregano extract into the caviar casting mixture.
2.4. Characterization of caviar substitutes (CS) 2.4.1. Proximate composition The proximate composition (moisture, protein, lipid, carbohydrate and ash) of the caviar substitutes were analyzed according to the standard procedure of AOAC (2000). 2.4.2. Determination of total yield The total yield of the sample was carried out by counting the number of caviar beads fully formed without tailing.
2. Materials and methods
Yield (%) =
2.1. Raw materials Fresh roes of Rohu ‘Labeo rohita’ were collected from a local fish market (Mumbai, India). The sodium alginate used in the study was of analytical grade and was obtained from Himedia (Mumbai, India). The oregano extract (OE) was procured from Synthite Industries Ltd (Kerala, India).
2.4.3. Scanning electron microscopy (SEM) The surface appearance and morphology of caviar substitutes was examined by SEM (XL 30 Philips, Eindhoven, Netherlands). Samples were fixed onto double-sided adhesive carbon tabs mounted on SEM stubs, coated with gold using a sputter coater.
2.2. Sample preparation
2.4.4. Fourier transform-infrared spectroscopic analysis (FT-IR) The FT-IR analysis of caviar substitutes was carried out using a Thermo Fisher Scientific FT-IR spectrometer (Model Nicolet™ iS™ 10, Thermo Fisher Scientific, Waltham, MA), in the wavelength range of 4000–400 cm−1. The spectra was analyzed using OMNIC software (Thermo Fisher Scientific, Waltham).
The alginate and fish roe suspension was prepared separately. The solution of roe and alginate were prepared at a total solid content of 5% (w/v) in the ratio 50:50, based on a separate optimization trial (data not given). To prepare the casting solution, freeze dried fish roe was homogenized to a uniform mixture using a high speed homogenizer. To this, alginate solution was added dropwise under continuous homogenization to get the final total solid content (fish roe and alginate together) of 5%. Prior to casting, oregano extract (Origanum vulgare) containing 43% (w/w) essential oil was added to the roe-alginate homogenate, at two different concentrations (0.5%, 1% w/w). The major components of OE as determined by Gas Chromatography-Mass Spectroscopic (GC-MS-MS) analysis were monoterpene hydrocarbons (20.86%), sesquiterpene hydrocarbons (5.32%), oxygenated monoterpenes (57.39%) and oxygenated sesquiterpenes (2.82%). The resultant mixture was dropped into a chilled calcium chloride (1% w/v) bath to obtain spherical caviar substitute beads. The entire experimental work was carried out at 25 ± 1 °C. After an initial reaction time of 30 min, the beads were drained and sealed in polyethylene pouches. Further, the biochemical, microbial and textural characteristics of the resultant caviar beads stored at 2 ± 1 °C were compared with caviars made without the addition of oregano extract.
2.4.5. Differential scanning calorimetry (DSC) The thermal characteristics of caviar substitutes were measured by DSC (Mettler Toledo TC15). Known amount of samples were weighed and placed in aluminum pans, heated at the rate of 10 °C/min, from −50 to 250 °C, under inert atmosphere (100 ml/min of N2) along with an empty pan as a reference. The freezing and melting curves were generated separately; the onset, peak, end set temperature and the enthalpy differences of the individual peaks were recorded. 2.4.6. Thermogravimetric/differential thermal analysis (TGA/DTA) Thermal analysis curves of the caviar substitutes were recorded in the temperature range of 30–750 °C at a heating rate of 10 °C/min using a Perkin Elmer STA 6000, Diamond TG/DTA system (PerkinElmer, Ohio, USA). 2.4.7. Determination of dimensional properties The dimensional properties such as weight average diameter (mm/ g) and number average weight (g/CS) were determined for 20 caviar beads from each sample. The diameter of individual caviar beads was measured using a calibrated caliper (Mitutoyo Absolute Digimatic Calipers, Model CSK 6″, Code No: 500-196-20).
2.3. Characterization of caviar forming solutions 2.3.1. Determination of specific gravity of caviar forming solutions 10 ml of the solution was poured into the measuring cylinder and the mass of the solution was noted. Similar experiment was carried out with distilled water. The specific gravity of the solution was calculated using the following formula: Specific gravity = mass of solution / mass of water
Weight of fully formed beads × 100 Weight of caviar casting solution
2.4.8. Determination of bulk density Bulk density (ρb) of caviar substitutes was determined in triplicate using a 25 ml glass measuring cylinder. Caviar samples were filled in a graduated measuring cylinder of known volume and the weight to volume ratio was determined. The bulk density values were reported as g/ ml.
(1)
2.3.2. Determination of viscosity profile of casting solutions The viscosity measurements were carried out at 25.0 ± 1 °C using LVDV-III ultra-programmable viscometer (Brook-field, USA). The caviar forming solutions were subjected to maturation at 25 °C for 1 h before measuring the viscosity at shear rate range of 10–100 s−1. The spindle was allowed to rotate for 1 min for stabilization and the time lapse between each shear rate increment was 10s. Three independent trials were carried out and the average viscosity values at each shear rate was plotted to obtain viscosity profile.
2.4.9. Determination of swelling index The swelling index was calculated based on the diameter of the samples before and after and suspending in water for 30 min at ambient temperature (27 °C). All the measurements were carried out in quintuplets. 447
LWT - Food Science and Technology 108 (2019) 446–455
P.K. Binsi, et al.
2.5. Chilled storage of caviar substitutes
flattening.
2.5.1. Biochemical analysis Proximate composition of homogenized samples was determined by AOAC (2000) method. The pH of the homogenized sample in distilled water (1: 5 w/v) was measured using a glass electrode digital pH meter (Cyberscan 510, Eutech instruments, Singapore). Total volatile base nitrogen (TVB-N) was estimated by the microdiffusion method (Conway, 1950). Oxidative stability of the sample was assessed by Thiobarbituric acid (TBARS) value (Tarladgis, Watts, Younathan, & Dugan, 1960) and peroxide value (PV) (Yildiz, Wehling, & Cuppett, 2003).
3.1.2. Specific gravity The specific gravity of the casting solution is a critical parameter for the proper immersion of droplets in the firming solution. The specific gravity of 1% CaCl2 solution was determined as 0.99 g/ml, hence slightly higher specific gravity than this values is desirable for the casting solution for proper immersion. The specific gravity of control caviar solution was found to be 1.07 g/ml (Table 1). Addition of OE resulted in a marginal reduction in specific gravity of caviar beads, to 1.05 and 1.02 mg/ml, respectively for 0.5% and 1% OE. The lower the specific gravity, the more the tendency of the casted droplets to float on the surface, which may lead to uneven hardening of roe-alginate mixture. On the other hand, denser solutions sink faster and settle down the bottom, which will again hinder the formation of the symmetrical beads. At the concentrations used in the present study, the specific gravity of casting mixture was high enough to suspend the droplets in the firming medium so as to facilitate even firming, yielding spherical caviar beads.
2.5.2. Microbiological analysis Microbiological analysis was carried out for the enumeration of total viable count (TVC), lactic acid bacteria (LAB), total Enterobacteriaceae and Escherichia coli (E. coli) as detailed previously (Binsi et al., 2014). 2.5.3. Texture profile analysis Texture analysis of the reconstituted caviars was determined by using Universal Testing Machine (Lloyd Instruments, LRX plus, UK) with Nexygen software. Each bead was compressed twice to 50% of the original height using a cylindrical probe having a diameter of 50 mm and a test speed of 5 mm/min.. The TPA of the randomly selected 10 samples were evaluated for each combination.
3.2. Characteristics of caviar substitutes Based on the optimization results (data not given), caviar substitutes were prepared by encapsulating 50:50 of freeze dried roe of Labeo rohita and sodium alginate at 5% total solid level, with varying concentrations of oregano extract viz. 0.5% (CS-0.5) and 1% (CS-1).
2.5.4. Sensory analysis Sensory analysis of raw and cooked samples was conducted by a panel of 6 experienced members based on predefined sensory attributes specific to caviar. A demerit scoring system from 9 to 0 was considered suitable for assessing the sensory parameters of caviar substitutes. From the scores obtained for each attribute, an overall acceptability score was derived by taking the average of individual scores.
3.2.1. Percentage tailing and yield The viscosity of the caviar casting solution is a critical parameter influencing the extent of tailing while dropping the solution into the firming medium. In the case of control caviar solution, tailing was completely absent, whereas a few tailed beads were observed in the case of OE added substitutes (Table 1). Among the OE substitutes, CS-1 showed slightly higher rate of tailing compared to CS-0.5, which might be on account of reduction in the specific gravity of casting solution with increase in OE in the casting solution. Interestingly, higher yield was observed by the addition of OE at 0.5% level, however reduced significantly when the concentration was increased to 1%. The yield was calculated based on the gravimetric method, and moreover, only uniformly spherical beads were considered for calculating the yield. Accordingly, the lower yield observed in CS-1 might be on account of the higher percentage of tailing and lesser entrapment of water.
2.5.5. Statistical analysis All experiments were done in triplicate (n = 3) and results were expressed as means ± standard deviation (SD). Further, the data were subjected to Analysis of Variance (ANOVA) by SPSS-16 at 5% level of significance. 3. Results and discussion
3.2.2. Scanning electron microscopy (SEM) The cross sectional characteristics of the freeze dried caviar substitutes indicated porous surface of micrometrical size (Fig. 1B). The control CS samples presented honeycomb like internal structure having an inner compact core with smaller pore size compared to the larger pores towards the surface. This is the typical structure of alginate beads, when ionic cross linkers such as CaCl2 is used, where the beads present a compact core compared to the porous crust. Presence of similar honeycomb like structure was reported by Stojanovic, BelscakCvitanovic, Manojlovic, Komes, Nedovic, & Bugarski (2012) where thyme (Thymus serpyllum L.) aqueous extract was encapsulated in calcium alginate beads. The pore diameter of the inner compact core was in the range of 178.89 μm to 242.07 μm while for the outer layer the pore diameter was 497.44 μm to 855.72 μm indicating the large size difference between pores of the inner and outer core. The SEM image indicated that the presence of roe components did not alter the normal cross-linking mechanism of alginate. Infact, the roe components were closely integrated within the alginate gel matrix either through physical or/and by chemical forces. Addition of oregano extract slightly altered the internal structure of beads which in turn gave different structural features at higher concentration of OE. The CS-0.5 samples showed uniformly structured honey comb pattern from crust to core congenial for the better retention of polyphenol mixture for an extended period
The properties of casting solutions viz. pH, viscosity, density, swelling and solubility in cross-linking solutions etc. largely affect the quality of caviars formed. Hence, the properties of casting solution and the set caviar substitutes with respect to the concentration of OE was evaluated. 3.1. Characteristics of caviar casting solution 3.1.1. Viscosity The viscosity of caviar casting solution is a critical parameter to ensure free dripping into the firming medium. The presence of essential oil may influence the structure and stability of emulsion and thereby the flow parameters of the casting solution. The viscosity profile of caviar casting solutions at both the concentrations of OE indicated nonNewtonian shear thinning behavior (Fig. 1A). However, towards higher shear rate a near Newtonian behavior was observed, which might be the typical behavior of roe proteins as also observed in our previous study (Binsi et al., 2017). A similar non-Newtonian shear thinning behavior was previously reported for alginate (Becker, Kipke, & Brandon, 2001). The viscosity of the casting solution is critical as less viscous solution flattens while dropping into the firming solution, before assuming a spherical shape. At the concentration used in this study, OE increased the fluidity of the mixture, however not to the level of caviar 448
LWT - Food Science and Technology 108 (2019) 446–455
P.K. Binsi, et al.
Fig. 1. A. Viscosity profile of caviar casting solutions. B-D. SEM images of caviar substitutes (B) CS (C) CS-0.5 (D) CS-1. E-F. FT-IR profile of caviar substitutes (E) CS (F) OE .
(Fig. 1C). Moreover, a well-defined radial distribution of the uniform sized pores with regular interconnections were evidenced. The observed symmetry in presence OE might be as a result of an organised orientation of roe-alginate components in presence of OE, which in turn favored an ordered compact orientation of alginate-roe protein in CaCl2 bath. Similar structural stabilization effect of sage polyphenols was observed in fish oil-gum arabic emulsion in our previous study (Binsi et al., 2017a). The pore diameter gave a narrower range of 172–363 μm, indicating the formation of smaller pores as compared to CS samples. In contrary, CS-1 presented an entirely different internal morphology from that of CS and CS-0.5 (Fig. 1D). The surface and core structure of CS-1 revealed the formation of a continuous matrix of closely packed horizontal ridges, without any distinct interconnections. The distance
between the ridges varied between 168.96 μm and 180.03 μm. The presence of ridges also created artefacts by collapsing the walls of pores during freeze-drying, and hence the beads appeared less spherical and shrunken. It appears that, higher concentration of OE destabilized the emulsion structure which in turn resulted in the formation of numerous localised areas of expansion (ice crystals) and contraction (most other constituents), leading to non-uniform change in volume in the continuous matrix. On the other hand, OE at 0.5% level improved the homogeneity of the system by forming a stable emulsion, which might have retained the typical micellar arrangement of hydrophilic and hydrophobic components during freeze drying. From the SEM images of caviar substitutes, it is logical to infer that addition of OE prior to the formation of the three-dimensional polymer matrix favored the 449
LWT - Food Science and Technology 108 (2019) 446–455
P.K. Binsi, et al.
asymmetric stretching vibration of C–H of CH3 and CH2 groups was not detectable in CS samples. This was also associated with the disappearance of absorption at 1590 cm−1, 1459 cm−1 and 1502 cm−1 in OE containing samples. A much prominent band at 1618 cm−1 and 1869 cm−1 in OE corresponding to carboxylate and five-membered aromatics, was totally absent in CS-0.5 and CS-1 samples, suggesting a possible modification of hydroxyl groups in the roe components and phenolic moieties in OE. The (-CH) band at 1414 cm−1 from the alginate component in CS remained almost unaltered in CS samples, however, the (C-O-C) band at 1033 cm−1 showed a shift to a higher wavelength of 1044 in CS-0.5. Coincidentally, a well-defined ester group was detectable at 1744 cm−1 in CS-0.5 sample which was not detectable in CS-1 and CS samples, which might have resulted from the interaction of terminal carboxyl group of alginate with phenolic components in OE. Generally, if COO- groups are involved in H-bonding a significant band broadening coupled with large shift to lower frequency is expected. However, in the case of essential oils, which contains volatile components, steric hindrance effect may be expected and the band may be observed at natural or higher frequencies (Coates, 2000). Previously, differing opinions about alginate-protein-polyphenol interactions were reported in literature (Chan Yim, Phan, Mansa, & Ravindra, 2010; Nadavala, Swayampakula, Boddu, & Abburi, 2009). In the present study, the alterations observed in the FT-IR profile of caviar samples suggest possible non-covalent interactions of OE with both alginate and roe components.
Table 1 Proximate composition and physico-chemical properties of caviar substitutes. Parameters
Mean Value CS
Moisture (g/100g) Protein (g/100g) Lipid (g/100g) Carbohydrate (g/100g) Ash (g/100g) Physico-chemical properties Yield (%) Tailing percentage (%) Weight average diameter (mm/g) Number average weight (g/ CS**) Bulk density (g/ml) Swelling index (%)
CS-0.5 a
a
CS-1
63.97 ± 0.43 15.43a ± 0.58 2.34a ± 0.71 12.32a ± 0.54 4.61a ± 0.12
61.82 ± 0.75 14.86 a ± 0.54 2.88a ± 0.62 11.53b ± 0.37 4.54a ± 0.23
61.07a ± 0.54 14.73 a ± 0.46 3.18a ± 0.52 11.17b ± 0.18 4.58a ± 0.18
79.70a ± 0.48 0 ± 0.02a 40.24a ± 2.51
82.39b ± 0.39 1.21b ± 0.05 38.73b ± 2.10
75.48c ± 0.81 1.42c ± 0.04 35.00c ± 3.48
0.17a ± 0.04
0.16a ± 0.01
0.18a ± 0.02
0.33a ± 0.08 48.27a ± 0.86
0.38b ± 0.06 60.78b ± 1.17
0.47c ± 0.02 26.25c ± 0.68
*Treatment mean values with same letters are not significantly different from each other (p < 0.05). **CS: Caviar substitute.
formation of beads with homogenous interconnected pores at 0.5% level. The presence of OE maintained the shape of the pores by imparting required hydrophobicity to the gel matrix and repulsion between the micelles and the carboxylate groups of the polymer chain. The results of SEM images further suggests the possibility of higher water entrapment in CS-0.5 as also confirmed by higher yield values of CS-0.5.
3.2.4. Differential scanning colorimetry (DSC) The thermal profile of caviar substitutes were analyzed by an initial cooling phase from 30 to −20 °C followed by a heating phase upto 260 °C above which the material started charring. In general, the thermograms showed a marginal shift in the thermal transition points (Fig. 2). Addition of OE resulted in the depression of freezing point of caviar substitutes from −19.5 °C peak temperature to −17.5 and −15.5 °C in CS-0.5 and CS-1, respectively. The heating curve indicated two distinct endothermic transitions corresponding to melting and denaturation of caviar components. The thermogram indicated slight reduction in peak temperature in CS-0.5 compared to CS, however almost double the value was shown by CS-1 sample. The second transition was comparatively a broader peak in all the samples, which might be a combined peak of volatile components in OE and moisture. Accordingly, the CS sample showed the onset temperature close to the boiling point of water, whereas OE containing samples showed lower values of 64.42 and 78.31 °C respectively, in CS-0.5 and CS-1 samples, respectively corresponding to the volatilization of OE components. The shift in transitional temperature coupled with significantly higher enthalpy of transition suggest the possible structural alterations occurred by the addition of OE in the casting mixture.
3.2.3. Fourier transform-infra red profile (FT-IR) The inclusion of OE markedly altered the FT-IR profile of caviar samples. The spectral behavior in the wavelength range of 3600–1400 cm−1 was analyzed in detail as it represents the characteristic stretching and bending vibrations of OH, COO-and NH groups that primarily contribute to protein-carbohydrate/protein-polyphenol/ carbohydrate-polyphenol interactions through hydrogen bonding. The FT-IR spectra showed the characteristic peaks of roe proteins at 1508 cm−1 and 1607 cm−1, respectively corresponding to the amide Ι (mainly C=O stretch) and II (C–N stretching coupled with N–H bending modes) peaks (Fig. 1E). The position of these peaks remained unaltered with the addition of OE, however, the amide II band was more prominent in OE incorporated samples, which otherwise showed lower peak intensity compared to amide-I in CS sample. This indicates the generation of more side-chain electrostatic interactions, more likely through hydrogen bonding, with the addition of OE. Generally, sodium alginate exhibits significant carbonyl stretching vibration at 1635 cm−1 corresponding to the carboxylate groups in the polymer (Saarai, Kasparkova, Sedlacek, & Saha, 2013). However, this band was appeared as a minor band with major shift towards the higher bandwidth of 1045 cm−1 in control and almost disappeared in OE containing samples, indicating the possibility of utilization of these moieties during the gelation process. Similarly, the major peak observed at 1717 cm−1 in OE corresponding to the carboxylic acid group was totally absent in CS0.5 whereas a less prominent peak was observed in CS-1 sample. These observations suggest the possible interactions of carboxylic group in OE with alginate or/and roe components. The amide A and B bands were not well differentiated in all the caviar samples. However, a band at 2967 was evident in CC which underwent slight shift towards the lower band width in CS samples. This suggests the possible interaction between roe protein and alginate in the caviar samples. The absorption in the broad wavelength range of 3200–3550 cm−1 observed in OE and CS, corresponding to the normal polymeric OH stretch and H-bonded OH stretch, was much condensed in OE containing samples, particularly in CS-1 (Fig. 1F). Similarly, the prominent absorption found in OE in the region of 2870–2970 cm−1 corresponding to the symmetric and
3.2.5. Thermogravimetric/differential thermal analysis (TGA/DTA) The thermal degradation profile of caviar substitutes could not be completely evolved by DSC in the given temperature range due to the interference from moisture as well as charring of the sample at higher temperatures. Hence, simultaneous TGA/DTA was carried out to evolve the degradation pattern of roe-alginate-polyphenol matrix of caviar substitutes. Generally, the thermal decomposition of polysaccharides is characterized by three transitional stages, viz. desorption of physically absorbed water, removal of structural water (dehydration reactions), depolymerisation accompanied by the rupture of C–O and C–C bonds in the ring units that cause the evolution of CO, CO2 and H2O, and finally the formation of polynuclear aromatic and graphitic carbon structures. The thermal analysis profile of both control and OE containing samples indicated four distinct regions of decompositional weight loss (Fig. 3). The initial weight loss observed below 200 °C range might be attributed mainly to the dehydration of the polymer network as this was also observed in polyphenol-free beads. The second major region of weight loss occurred at around 220 °C corresponds to the release of 450
LWT - Food Science and Technology 108 (2019) 446–455
P.K. Binsi, et al.
Fig. 2. A-F. DSC profile of caviar substitutes.
cooking or boiling temperatures, in all the caviar samples. The lower temperatures of decomposition observed for CS-1 in all the transition peaks might be indicative of the formation of a poor gel network in CS1. It should be mentioned that no separate transition peak corresponding to OE was visible in OE containing samples. This further implies that the added OE interacted with roe and alginate components to a greater extent, as also inferred from the FT-IR profile.
decomposition of shorter peptides in the fish roe as well as the polyphenols in oregano extract. Accordingly, highest peak intensity (maximum weight loss) was observed in CS-1 and was much condensed in control CS sample. The higher weight loss observed in OE containing sample in the first transition suggest the loss of unreacted OE as well, as the weight loss was more in CS-1 sample. The third transition point observed at around 280 °C in the DTA curve might be due to the decomposition of roe-alginate network and pure alginate components forming carbonaceous materials. Consequent to this a fourth stage of weight loss appeared in the thermogram at around 320–330 °C due to the loss of carbonaceous material from the sample. In general, The CS and CS-0.5 samples showed similar pattern of decomposition, whereas the CS-1 showed higher rate of decomposition with slightly lower volatilization temperature at all transition peaks. However, the thermograms confirmed the stability and availability of caviar constituents at
3.2.6. Dimensional properties of reconstituted caviar The dimensional properties of set caviars are important as it also indicates the extent of firming, compactness and the size uniformity of the beads. Addition of OE resulted in a slight reduction in the weight average diameter (mm/g) of OE containing caviar, whereas the average unit weight showed slightly higher value for CS-1 (Table 1). The reduction in the average diameter coupled with the increase in the 451
LWT - Food Science and Technology 108 (2019) 446–455
P.K. Binsi, et al.
Fig. 3. A-C. TGA/DTA profile of caviar substitutes.
average weight in OE samples indicates the formation of a compact network with minimum entrapment of water in OE containing samples owing to the hydrophobicity offered by OE, as also revealed from the SEM images.
3.2.7. Bulk density The bulk density values of caviar substitutes were significantly increased (p < 0.05) by the incorporation of OE in the casting solution (Table 1). This might be due to the significant reduction in the average dimension of the caviar beads owing to the formation of more compact matrix. The significantly higher bulk density observed in CS-1 samples 452
LWT - Food Science and Technology 108 (2019) 446–455
P.K. Binsi, et al.
indicates a more or less solid internal structure with minimum porosity as also confirmed by SEM images.
increases with a reduction in pH of the food, since at low pH the hydrophobicity of the oil increases, enabling it to more easily dissolve in the lipids of cell membrane of the target bacteria (Burt, 2004). Previously (Lin, Labbe, & Shetty, 2004), a marginal inhibitory effect was reported on Listeria monocytogenes in beef and fish slices in presence of oregano and cranberry extract even after 18 h at pH 7, whereas significant differences in viable cell counts were observed at pH 6.0. In the present study, in both the treated samples, pH remained below or almost equal to 6 till the end of chilled storage, whereas that of control CS crossed 6 after 16th day.
3.2.8. Swelling index The diameter of the caviar before and after suspending in aqueous media was evaluated to assess any dimensional alterations. Both control and OE added samples retained the integrity in aqueous media even after dipping for 30 min. However, distinct difference in the diameter of the beads were observed, with a significant extent of swelling in CS-0.5 whereas CS-1 showed a much lower value compared to control CS samples (Table 1). This might be due to the formation of regular porous internal structure of CS-0.5 congenial for better diffusion and entrapment of water molecules, compared to the random plated structure of CS-1. The results of dimensional properties are also in agreement with the structural features derived from SEM, FT-IR and thermal analysis.
3.3.2. Total volatile base - nitrogen (TVB-N) The mean TVB-N values of caviar samples during chilled storage period indicated significant difference between the control and OE treated samples (p < 0.05) (Fig. 4B). Treatment with OE was found to be more effective in delaying TVB-N formation during chilled storage, which may be attributed to the antimicrobial property of the phenolic constituents in oregano extract as observed in our previous study (Binsi et al., 2016). The mean TVB-N values of caviar samples over the period of chilled storage indicated significantly lower mean values for OE treated samples (p < 0.05). The TVB-N values increased rapidly after 4th day of chilled storage in control caviar samples, whereas OE treated samples showed minimum generation of volatile base nitrogen compounds (VB-N) throughout the chilled storage period.
3.3. Changes during chilled storage 3.3.1. pH pH values showed increasing trend throughout the storage period, with lower absolute values for samples containing OE as compared to control (Fig. 4A). As storage period progressed, pH of control sampleincreased by more than 1 pH unit, whereas in CS-0.5 and CS-1, an increase of only 0.23 and 0.25 units respectively was observed. This might be attributed to the antibacterial properties of oregano extract which retarded the decomposition of protein substrate into amino acids and short peptides. The bacterial susceptibility to essential oils
3.3.3. Lipid oxidation indices The PV rose sharply during the initial 7 days of storage in control Fig. 4. A-F. Changes in (A) pH (B) TVB-N (C) PV (D) TBARS (E) TVC (F) Enterobacteriaceae count of caviar substitutes.
453
LWT - Food Science and Technology 108 (2019) 446–455
P.K. Binsi, et al.
samples, with a peak value on 8th day of chilled storage (p < 0.05) (Fig. 4C). A slower increase in PV was observed in OE treated samples, demonstrating the higher oxidative stability of roe lipids during chilled storage in the presence of OE. Generally, peroxide value between 5 and 10 mEq/kg indicates the commencement of rancidity. In the present study, CS sample crossed 5 mEq/kg on 4th day of storage, whereas PV of OE treated samples were well below the limit throughout the storage period. The TBARS values of CS sample crossed the limit of 2 mg of MDA/kg (Connel, 1995, p. 241), after 4th day of storage indicating the onset of oxidative rancidity (Fig. 5D). In OE treated samples, TBARS values followed almost similar pattern at both the concentrations, and remained well below this range throughout the storage period. The protective effect of oregano essential oil, mint leaf extract and essential oils of clove and curry leaf on chill stored fish and fish oil encapsulates by minimizing the generation of peroxy free radicals was demonstrated in our previous studies (Binsi et al., 2016, 2017a; Jeyakumari, Zynudheen, Binsi, Parvathy, & Ravishankar, 2017; Viji et al., 2016). In the present study, the protective effect was evident at a lower concentration of 0.5% and doubling the concentration further did not contribute significantly (p < 0.05) to the protective mechanism.
log cfu/g till the end of the study (Fig. 4E). On the contrary, CS-1 samples indicated less than a unit log increase in TVC till the end of storage period, which might be related to the higher content of free essential oil in the caviar matrix. Zinoviadou, Koutsoumanis, and Biliaderis (2009) reported that 1.5% oregano essential oil incorporated whey protein isolate edible films resulted in 3.3 log reduction of TVC on fresh beef cuts as compared to the control sample on 8th day of refrigerated storage. In the present study, the control samples were rejected on 27th day of chilled storage, whereas preservative effect was observed even at 0.5% level eventhough 1% OE had a better protective effect. Enterobacteriaceae and E. coli counts are often used to assess the overall hygiene status of the processing operations and the temperature history of the product during storage. In the present study, Enterobacteriaceae was not detectable in OE treated samples, however it was present in control caviar samples (Fig. 4F). Escherichia coli was not detected in any of the samples throughout the chilled storage period, indicating that the roe was not contaminated with gut content of fish during gutting and cleaning steps. Apart from that, this also indicates the best management practices followed in the aquaculture farm.
3.3.4. Microbiological parameters During chilled storage, bacterial growth progressed much faster in control caviar samples compared to OE treated samples, as indicated by the higher microbial count in CS from 1st day of storage onwards (Fig. 4E & F). TVC of CS-0.5 samples showed a progressive increase during the storage period, however, the count remained well below 4
3.3.5. Texture profile analysis (TPA) The texture profile values indicated only marginal variation between the samples during initial period of chilled storage (Fig. 5). The fresh samples of caviar substitutes showed almost similar hardness values, whereas a slight hardening effect was observed in OE samples Fig. 5. A-F. Changes in TPA profile of caviar substitutes.
454
LWT - Food Science and Technology 108 (2019) 446–455
P.K. Binsi, et al.
on the third day of chilled storage. Among the samples, slightly lower hardness value was observed for CS-1 samples initially, probably because of the higher content of OE, which might have interfered with the roe-alginate network formation. However, the value increased during subsequent days of storage similar to CS-0.5 sample. The control sample showed a progressive reduction in the hardness values during the storage period, whereas that of OE samples remained almost stable till the end of the study. The hardness-2 values showed distinct differences between the samples after 1st day of storage, with significantly lower values for control samples. This implies the matrix stabilizing effect of OE, by way of structural modification. Similar changes were observed in all the other parameters, with higher springiness, chewiness, cohesiveness and stiffness values for OE treated samples, particularly during the latter period of storage. The changes in the texture profile of caviar substitutes further confirms the structure stabilization effect of OE via protein/alginate–polyphenol interactions. However, only marginal difference was observed between CS-0.5 and CS-1 samples during chilled storage.
doi.org/10.1016/j.lwt.2019.03.001. References AOAC (2000). Official methods of analysis of association of official analytical chemists international, 17th, suite 500,481,North frederick avenue, Gaithersburg, Maryland 208772417, USA. Becker, T. A., Kipke, D. R., & Brandon, T. (2001). Calcium alginate gel: A biocompatible and mechanically stable polymer for endovascular embolization. Journal of Biomedical Materials Research Part A, 54(1), 76–86. Binsi, P. K., Natasha, N., Sarkar, P. C., Ashraf, P. M., George, N., & Ravishankar, C. N. (2017). Structural, functional and in vitro digestion characteristics of spray dried fish roe powder stabilised with gum Arabic. Food Chemistry, 221, 1698–1708. Binsi, P. K., Nayak, N., Sarkar, P. C., Jeyakumari, A., Muhamed Ashraf, P., Ninan, G., et al. (2017a). Structural and oxidative stabilization of spray dried fish oil microencapsulates with gum Arabic and sage polyphenols: Characterization and release kinetics. Food Chemistry, 219, 158–168. Binsi, P. K., Ninan, G., & Ravishankar, C. N. (2017b). Effect of curry leaf and clove bud essential oils on textural and oxidative stability of chill stored sutchi catfish fillets. Journal of Texture Studies, 48(3), 258–266. Binsi, P. K., Ninan, G., Zynudheen, A. A., Neethu, R., Ronda, V., & Ravishankar, C. N. (2014). Compositional and chill storage characteristics of microwave‐blanched sutchi catfish (Pangasianodon hypophthalmus) fillets. International Journal of Food Science and Technology, 49(2), 364–372. Binsi, P. K., Ravishankar, C. N., Mathew, S. S., Athira, V. P., Biji, K. B., Joshy, C. G., et al. (2016). Comparative evaluation of natural antioxidant coating and vacuum-packaging technique on quality characteristics of chill stored giant trevally fillets. Journal of Aquatic Food Product Technology, 25(2), 197–209. Binsi, P. K., Viji, P., Panda, S. K., Mathew, S., Zynudheen, A. A., & Ravishankar, C. N. (2016a). Characterisation of hydrolysates prepared from engraved catfish (Nemapteryx caelata) roe by serial hydrolysis. Journal of Food Science and Technology, 53(1), 158–170. Burt, S. (2004). Essential oils: their antibacterial properties and potential applications in foods—a review. International Journal of Food Microbiology, 94(3), 223–253. Chan, E. S., Yim, Z. H., Phan, S. H., Mansa, R. F., & Ravindra, P. (2010). Encapsulation of herbal aqueous extract through absorption with ca-alginate hydrogel beads. Food and Bioproducts Processing, 88(2), 195–201. Coates, J. (2000). Interpretation of infrared spectra, a practical approach. Encyclopedia of analytical chemistry. Connel, J. J. (1995). Control of fish quality. Cambridge, London: Fishing New Books. Blackwell Science Ltd. Conway, E. J. (1950). Micro-diffusion analysis and volumetric error. Crosby. London: Lockwood and Son Ltd. Daemi, H., & Barikani, M. (2012). Synthesis and characterization of calcium alginate nanoparticles, sodium homopolymannuronate salt and its calcium nanoparticles. Scientia Iranica, 19, 2023–2028. Jeyakumari, A., Zynudheen, A. A., Binsi, P. K., Parvathy, U., & Ravishankar, C. N. (2017). Microencapsulation of fish oil-oregano essential oil blends by spray drying and its oxidative stability. Journal of Agricultural Science and Technology A, 19, 1539–1550. Klokk, T. I., & Melvik, J. E. (2002). Controlling the size of alginate gel beads by use of a high electrostatic potential. Journal of Microencapsulation, 19, 415–424. Lin, Y. T., Labbe, R. G., & Shetty, K. (2004). Inhibition of Listeria monocytogenes in fish and meat systems by use of oregano and cranberry phytochemical synergies. Applied and Environmental Microbiology, 70(9), 5672–5678. Nadavala, S. K., Swayampakula, K., Boddu, V. M., & Abburi, K. (2009). Biosorption of phenol and o-chlorophenol from aqueous solutions on to chitosan–calcium alginate blended beads. Journal of Hazardous Materials, 162(1), 482–489. Saarai, A., Kasparkova, V., Sedlacek, T., & Sáha, P. (2013). On the development and characterisation of crosslinked sodium alginate/gelatine hydrogels. Journal of the Mechanical Behavior of Biomedical Materials, 18, 152–166. Stojanovic, R., Belscak‐Cvitanovic, A., Manojlovic, V., Komes, D., Nedovic, V., & Bugarski, B. (2012). Encapsulation of thyme (Thymus serpyllum L.) aqueous extract in calcium alginate beads. Journal of the Science of Food and Agriculture, 92(3), 685–696. Tarladgis, B. G., Watts, B. M., Younathan, M. T., & Dugan, L. (1960). A distillation method for quantitative determination of malonaldehyde in rancid foods. Journal of the American Oil Chemists’ Society, 37, 44–48. Viji, P., Binsi, P. K., Visnuvinayagam, S., Bindu, J., Ravishankar, C. N., & Gopal, T. K. S. (2015). Efficacy of mint (Mentha arvensis) leaf and citrus (Citrus aurantium) peel extracts as natural preservatives for shelf life extension of chill stored Indian mackerel. Journal of Food Science and Technology, 52(10), 6278–6289. Viji, P., Binsi, P. K., Visnuvinayagam, S., Ravishankar, C. N., Venkateshwarlu, G., & Gopal, T. K. S. (2016). Modified icing system containing mint leaf and citrus peel extracts: Effects on quality changes and shelf life of Indian mackerel. Indian Journal of Fisheries, 63(2), 93–101. Yildiz, G., Wehling, R. L., & Cuppett, S. L. (2003). Comparison of four analytical methods for the determination of peroxide value in oxidized soybean oils. Journal of the American Oil Chemists’ Society, 80, 103–107. Zinoviadou, K. G., Koutsoumanis, K. P., & Biliaderis, C. G. (2009). Physico-chemical properties of whey protein isolate films containing oregano oil and their antimicrobial action against spoilage flora of fresh beef. Meat Science, 82(3), 338–345.
3.3.6. Sensory evaluation of caviar substitutes The sensory acceptability is an important parameter for evaluating the quality of caviar substitute as there exist well defined grading systems for caviar and caviar related products, which is even specific to the individual fish species in the International market. However, as there is no standard specifications for carp caviar (as it originally exist as gelly like mass), the general descriptions for scoring caviar products was followed. Accordingly, higher sensory score was obtained for CS-0.5 followed by CS (Fig. S1). The CS-1 scored less in particular for texture compared to other two samples. The CS-0.5 presented soft and spongy texture, whereas control CS samples presented grittiness towards the core. Apart from that control samples exhibited stickiness posing difficulty in mastication. The CS-1 samples were less spongy and hard in texture, presenting uneasiness while chewing. Moreover, the flavor of oregano was more predominant in CS-1 samples, and scored less for flavor attribute. 4. Conclusion The chilled storage stability of caviar substitute prepared from carp roe mass was evaluated. Addition of oregano extract at 0.5% improved the textural and sensory properties of caviar substitutes. Further, the addition of oregano extract improved the chilled storage stability of caviar substitutes in terms of oxidative and microbial parameters. A possible correlation between the polyphenol-roe-alginate interaction and textural stabilization was derived. The current study identifies the potential of utilizing carp roe by converting to novel high value products such as fish caviars with suitable stabilizers such as plant polyphenols. Conflicts of interest The authors have no conflicts of interest to declare. Acknowledgement This work was carried out under the research project jointly supported by Science and Engineering Research Board SERB (Department of Science and Technology, India) and MOFPI (Ministry of Food Processing Industries, India). Appendix A. Supplementary data Supplementary data to this article can be found online at https://
455
Contents lists available at ScienceDirect
LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt
Conversion of carp roe mass to caviar substitutes: Stabilization with oregano extract
T
P.K. Binsia,∗, Natasha Nayaka, P.C. Sarkarb,1, Upali Sahub,1, K.V. Lalithaa, George Ninana, C.N. Ravishankara a b
ICAR- Central Institute of Fisheries Technology, Matsyapuri, Willingdon Island, Cochin, 682 029, India ICAR - Indian Institute of Natural Resins and Gums, Namkum, Ranchi, 834 010, India
ARTICLE INFO
ABSTRACT
Keywords: Caviar substitutes Carp roe Oregano extract Alginate Chilled storage
Fish roe is a nutritionally rich source of polyunsaturated fatty acids, essential amino acids and several vitamins. However, its utilization is currently limited to caviars from a few fish species, as most of others form a jelly mass on cooking. In the present study, freeze dried carp roe mass was converted to caviar substitutes by reconstituting with sodium alginate. Further, oregano extract was added at different concentrations to the mixture as antioxidant and antimicrobial agent before casting. Scanning electron microscopic image revealed a honey-comb like structure for the freeze dried caviar samples, congenial for the retention of oregano extract for an extended period. DSC profile of caviar substitutes confirmed the stability and availability of caviar constituents at boiling temperature. Further, the biochemical, microbial and textural characteristics of caviar substitutes during storage at 4 °C indicated lower bacterial count and minimum generation of lipid oxidation products in caviar substitutes containing 0.5% oregano extract.
1. Introduction Fish roe is a nutritionally rich component, which are usually discarded as waste during processing operations. The contribution of roe to the whole body weight of carps may be as high as 30% during spawning seasons. The superior nutritional value of fish roe arises from its unique amino acid profile coupled with the high content of polyunsaturated fatty acids such as EPA and DHA, and vitamin B. The major amino acids are glutamic acid, leucine, proline, lysine and aspartic acid, and is poor in methionine, cysteine, tyrosine and tryptophan (Binsi et al., 2016a). However, these compositional features are also responsible for the fast spoilage of fish roe during storage due to microbial and oxidative changes. Caviar is a high value delicacy made from fish roe by treating with food grade salt. The term ‘caviar’ is conventionally reserved to certain varieties of fish roe, popularly from the members of Acipenseridae Family (Acipenser sp.), sturgeon fish. Over time, the overexploitation of sturgeons for caviar processing has led to the fast depletion of sturgeon population. Hence, there is high demand for simulated/imitation caviar alternatives prepared using roe from easily available fish species including farmed fishes. Researchers are continuously putting effort in
this line for alternative forms such as simulated caviar, caviar substitutes, reconstituted caviar etc. Eventhough, these alternative forms resemble caviar in appearance and sensory perception, they may contain components other than fish roe, such as gelling and flavouring agents. Alginates are commonly employed gelling agents, which are primarily isolated from brown algae. Previously, the preparation of caviar substitutes by dripping the homogenate of fish roe and alginate into a divalent solution was reported by a couple of researchers (Daemi & Barikani, 2012; Klokk & Melvik, 2002). However, the shelf life of such preparations are limited to a few days under chilled condition. The high PUFA content of fish roe makes it highly susceptible for auto-oxidation and the high free amino acid content enhances microbial degradation. Generally, caviars are considered as cured products containing high proportion of salt, which primarily acts as the preservatory agent. However, due to health reasons alternative preservation strategies are in demand. Plant extracts are rich in polyphenols and several other bioactive substances, which serve as potent antioxidant and antibacterial agents. The protective effect of oregano extract and a few other plant extracts as antioxidant, antibacterial as well as texture modifying agent was observed in our earlier studies (Binsi et al., 2016;
Corresponding author. E-mail address: [email protected] (P.K. Binsi). 1 Present address: National Institute of Research on Jute and allied fibre technology ICAR-NIRJAFT, 12 Regent Park, Tollygunge, Kolkata – 700040. ∗
https://doi.org/10.1016/j.lwt.2019.03.001 Received 23 November 2018; Received in revised form 27 February 2019; Accepted 1 March 2019 Available online 13 March 2019 0023-6438/ © 2019 Elsevier Ltd. All rights reserved.
LWT - Food Science and Technology 108 (2019) 446–455
P.K. Binsi, et al.
Binsi et al., 2017a; Binsi, Ninan, & Ravishankar, 2017b; Viji, Binsi, Visnuvinayagam, Ravishankar, Venkateshwarlu, & Gopal., 2015). Hence, in the present study oregano extract was added at various levels to the roe-alginate mixture prior to casting, and the antioxidant, antibacterial, and texture modifying effects was evaluated. Based on our previous observations, the hypothesis of the present study was that, the inferior texture and the limited shelf life of fish roe based products such as caviar substitute may be improved by incorporating polyphenol rich oregano extract into the caviar casting mixture.
2.4. Characterization of caviar substitutes (CS) 2.4.1. Proximate composition The proximate composition (moisture, protein, lipid, carbohydrate and ash) of the caviar substitutes were analyzed according to the standard procedure of AOAC (2000). 2.4.2. Determination of total yield The total yield of the sample was carried out by counting the number of caviar beads fully formed without tailing.
2. Materials and methods
Yield (%) =
2.1. Raw materials Fresh roes of Rohu ‘Labeo rohita’ were collected from a local fish market (Mumbai, India). The sodium alginate used in the study was of analytical grade and was obtained from Himedia (Mumbai, India). The oregano extract (OE) was procured from Synthite Industries Ltd (Kerala, India).
2.4.3. Scanning electron microscopy (SEM) The surface appearance and morphology of caviar substitutes was examined by SEM (XL 30 Philips, Eindhoven, Netherlands). Samples were fixed onto double-sided adhesive carbon tabs mounted on SEM stubs, coated with gold using a sputter coater.
2.2. Sample preparation
2.4.4. Fourier transform-infrared spectroscopic analysis (FT-IR) The FT-IR analysis of caviar substitutes was carried out using a Thermo Fisher Scientific FT-IR spectrometer (Model Nicolet™ iS™ 10, Thermo Fisher Scientific, Waltham, MA), in the wavelength range of 4000–400 cm−1. The spectra was analyzed using OMNIC software (Thermo Fisher Scientific, Waltham).
The alginate and fish roe suspension was prepared separately. The solution of roe and alginate were prepared at a total solid content of 5% (w/v) in the ratio 50:50, based on a separate optimization trial (data not given). To prepare the casting solution, freeze dried fish roe was homogenized to a uniform mixture using a high speed homogenizer. To this, alginate solution was added dropwise under continuous homogenization to get the final total solid content (fish roe and alginate together) of 5%. Prior to casting, oregano extract (Origanum vulgare) containing 43% (w/w) essential oil was added to the roe-alginate homogenate, at two different concentrations (0.5%, 1% w/w). The major components of OE as determined by Gas Chromatography-Mass Spectroscopic (GC-MS-MS) analysis were monoterpene hydrocarbons (20.86%), sesquiterpene hydrocarbons (5.32%), oxygenated monoterpenes (57.39%) and oxygenated sesquiterpenes (2.82%). The resultant mixture was dropped into a chilled calcium chloride (1% w/v) bath to obtain spherical caviar substitute beads. The entire experimental work was carried out at 25 ± 1 °C. After an initial reaction time of 30 min, the beads were drained and sealed in polyethylene pouches. Further, the biochemical, microbial and textural characteristics of the resultant caviar beads stored at 2 ± 1 °C were compared with caviars made without the addition of oregano extract.
2.4.5. Differential scanning calorimetry (DSC) The thermal characteristics of caviar substitutes were measured by DSC (Mettler Toledo TC15). Known amount of samples were weighed and placed in aluminum pans, heated at the rate of 10 °C/min, from −50 to 250 °C, under inert atmosphere (100 ml/min of N2) along with an empty pan as a reference. The freezing and melting curves were generated separately; the onset, peak, end set temperature and the enthalpy differences of the individual peaks were recorded. 2.4.6. Thermogravimetric/differential thermal analysis (TGA/DTA) Thermal analysis curves of the caviar substitutes were recorded in the temperature range of 30–750 °C at a heating rate of 10 °C/min using a Perkin Elmer STA 6000, Diamond TG/DTA system (PerkinElmer, Ohio, USA). 2.4.7. Determination of dimensional properties The dimensional properties such as weight average diameter (mm/ g) and number average weight (g/CS) were determined for 20 caviar beads from each sample. The diameter of individual caviar beads was measured using a calibrated caliper (Mitutoyo Absolute Digimatic Calipers, Model CSK 6″, Code No: 500-196-20).
2.3. Characterization of caviar forming solutions 2.3.1. Determination of specific gravity of caviar forming solutions 10 ml of the solution was poured into the measuring cylinder and the mass of the solution was noted. Similar experiment was carried out with distilled water. The specific gravity of the solution was calculated using the following formula: Specific gravity = mass of solution / mass of water
Weight of fully formed beads × 100 Weight of caviar casting solution
2.4.8. Determination of bulk density Bulk density (ρb) of caviar substitutes was determined in triplicate using a 25 ml glass measuring cylinder. Caviar samples were filled in a graduated measuring cylinder of known volume and the weight to volume ratio was determined. The bulk density values were reported as g/ ml.
(1)
2.3.2. Determination of viscosity profile of casting solutions The viscosity measurements were carried out at 25.0 ± 1 °C using LVDV-III ultra-programmable viscometer (Brook-field, USA). The caviar forming solutions were subjected to maturation at 25 °C for 1 h before measuring the viscosity at shear rate range of 10–100 s−1. The spindle was allowed to rotate for 1 min for stabilization and the time lapse between each shear rate increment was 10s. Three independent trials were carried out and the average viscosity values at each shear rate was plotted to obtain viscosity profile.
2.4.9. Determination of swelling index The swelling index was calculated based on the diameter of the samples before and after and suspending in water for 30 min at ambient temperature (27 °C). All the measurements were carried out in quintuplets. 447
LWT - Food Science and Technology 108 (2019) 446–455
P.K. Binsi, et al.
2.5. Chilled storage of caviar substitutes
flattening.
2.5.1. Biochemical analysis Proximate composition of homogenized samples was determined by AOAC (2000) method. The pH of the homogenized sample in distilled water (1: 5 w/v) was measured using a glass electrode digital pH meter (Cyberscan 510, Eutech instruments, Singapore). Total volatile base nitrogen (TVB-N) was estimated by the microdiffusion method (Conway, 1950). Oxidative stability of the sample was assessed by Thiobarbituric acid (TBARS) value (Tarladgis, Watts, Younathan, & Dugan, 1960) and peroxide value (PV) (Yildiz, Wehling, & Cuppett, 2003).
3.1.2. Specific gravity The specific gravity of the casting solution is a critical parameter for the proper immersion of droplets in the firming solution. The specific gravity of 1% CaCl2 solution was determined as 0.99 g/ml, hence slightly higher specific gravity than this values is desirable for the casting solution for proper immersion. The specific gravity of control caviar solution was found to be 1.07 g/ml (Table 1). Addition of OE resulted in a marginal reduction in specific gravity of caviar beads, to 1.05 and 1.02 mg/ml, respectively for 0.5% and 1% OE. The lower the specific gravity, the more the tendency of the casted droplets to float on the surface, which may lead to uneven hardening of roe-alginate mixture. On the other hand, denser solutions sink faster and settle down the bottom, which will again hinder the formation of the symmetrical beads. At the concentrations used in the present study, the specific gravity of casting mixture was high enough to suspend the droplets in the firming medium so as to facilitate even firming, yielding spherical caviar beads.
2.5.2. Microbiological analysis Microbiological analysis was carried out for the enumeration of total viable count (TVC), lactic acid bacteria (LAB), total Enterobacteriaceae and Escherichia coli (E. coli) as detailed previously (Binsi et al., 2014). 2.5.3. Texture profile analysis Texture analysis of the reconstituted caviars was determined by using Universal Testing Machine (Lloyd Instruments, LRX plus, UK) with Nexygen software. Each bead was compressed twice to 50% of the original height using a cylindrical probe having a diameter of 50 mm and a test speed of 5 mm/min.. The TPA of the randomly selected 10 samples were evaluated for each combination.
3.2. Characteristics of caviar substitutes Based on the optimization results (data not given), caviar substitutes were prepared by encapsulating 50:50 of freeze dried roe of Labeo rohita and sodium alginate at 5% total solid level, with varying concentrations of oregano extract viz. 0.5% (CS-0.5) and 1% (CS-1).
2.5.4. Sensory analysis Sensory analysis of raw and cooked samples was conducted by a panel of 6 experienced members based on predefined sensory attributes specific to caviar. A demerit scoring system from 9 to 0 was considered suitable for assessing the sensory parameters of caviar substitutes. From the scores obtained for each attribute, an overall acceptability score was derived by taking the average of individual scores.
3.2.1. Percentage tailing and yield The viscosity of the caviar casting solution is a critical parameter influencing the extent of tailing while dropping the solution into the firming medium. In the case of control caviar solution, tailing was completely absent, whereas a few tailed beads were observed in the case of OE added substitutes (Table 1). Among the OE substitutes, CS-1 showed slightly higher rate of tailing compared to CS-0.5, which might be on account of reduction in the specific gravity of casting solution with increase in OE in the casting solution. Interestingly, higher yield was observed by the addition of OE at 0.5% level, however reduced significantly when the concentration was increased to 1%. The yield was calculated based on the gravimetric method, and moreover, only uniformly spherical beads were considered for calculating the yield. Accordingly, the lower yield observed in CS-1 might be on account of the higher percentage of tailing and lesser entrapment of water.
2.5.5. Statistical analysis All experiments were done in triplicate (n = 3) and results were expressed as means ± standard deviation (SD). Further, the data were subjected to Analysis of Variance (ANOVA) by SPSS-16 at 5% level of significance. 3. Results and discussion
3.2.2. Scanning electron microscopy (SEM) The cross sectional characteristics of the freeze dried caviar substitutes indicated porous surface of micrometrical size (Fig. 1B). The control CS samples presented honeycomb like internal structure having an inner compact core with smaller pore size compared to the larger pores towards the surface. This is the typical structure of alginate beads, when ionic cross linkers such as CaCl2 is used, where the beads present a compact core compared to the porous crust. Presence of similar honeycomb like structure was reported by Stojanovic, BelscakCvitanovic, Manojlovic, Komes, Nedovic, & Bugarski (2012) where thyme (Thymus serpyllum L.) aqueous extract was encapsulated in calcium alginate beads. The pore diameter of the inner compact core was in the range of 178.89 μm to 242.07 μm while for the outer layer the pore diameter was 497.44 μm to 855.72 μm indicating the large size difference between pores of the inner and outer core. The SEM image indicated that the presence of roe components did not alter the normal cross-linking mechanism of alginate. Infact, the roe components were closely integrated within the alginate gel matrix either through physical or/and by chemical forces. Addition of oregano extract slightly altered the internal structure of beads which in turn gave different structural features at higher concentration of OE. The CS-0.5 samples showed uniformly structured honey comb pattern from crust to core congenial for the better retention of polyphenol mixture for an extended period
The properties of casting solutions viz. pH, viscosity, density, swelling and solubility in cross-linking solutions etc. largely affect the quality of caviars formed. Hence, the properties of casting solution and the set caviar substitutes with respect to the concentration of OE was evaluated. 3.1. Characteristics of caviar casting solution 3.1.1. Viscosity The viscosity of caviar casting solution is a critical parameter to ensure free dripping into the firming medium. The presence of essential oil may influence the structure and stability of emulsion and thereby the flow parameters of the casting solution. The viscosity profile of caviar casting solutions at both the concentrations of OE indicated nonNewtonian shear thinning behavior (Fig. 1A). However, towards higher shear rate a near Newtonian behavior was observed, which might be the typical behavior of roe proteins as also observed in our previous study (Binsi et al., 2017). A similar non-Newtonian shear thinning behavior was previously reported for alginate (Becker, Kipke, & Brandon, 2001). The viscosity of the casting solution is critical as less viscous solution flattens while dropping into the firming solution, before assuming a spherical shape. At the concentration used in this study, OE increased the fluidity of the mixture, however not to the level of caviar 448
LWT - Food Science and Technology 108 (2019) 446–455
P.K. Binsi, et al.
Fig. 1. A. Viscosity profile of caviar casting solutions. B-D. SEM images of caviar substitutes (B) CS (C) CS-0.5 (D) CS-1. E-F. FT-IR profile of caviar substitutes (E) CS (F) OE .
(Fig. 1C). Moreover, a well-defined radial distribution of the uniform sized pores with regular interconnections were evidenced. The observed symmetry in presence OE might be as a result of an organised orientation of roe-alginate components in presence of OE, which in turn favored an ordered compact orientation of alginate-roe protein in CaCl2 bath. Similar structural stabilization effect of sage polyphenols was observed in fish oil-gum arabic emulsion in our previous study (Binsi et al., 2017a). The pore diameter gave a narrower range of 172–363 μm, indicating the formation of smaller pores as compared to CS samples. In contrary, CS-1 presented an entirely different internal morphology from that of CS and CS-0.5 (Fig. 1D). The surface and core structure of CS-1 revealed the formation of a continuous matrix of closely packed horizontal ridges, without any distinct interconnections. The distance
between the ridges varied between 168.96 μm and 180.03 μm. The presence of ridges also created artefacts by collapsing the walls of pores during freeze-drying, and hence the beads appeared less spherical and shrunken. It appears that, higher concentration of OE destabilized the emulsion structure which in turn resulted in the formation of numerous localised areas of expansion (ice crystals) and contraction (most other constituents), leading to non-uniform change in volume in the continuous matrix. On the other hand, OE at 0.5% level improved the homogeneity of the system by forming a stable emulsion, which might have retained the typical micellar arrangement of hydrophilic and hydrophobic components during freeze drying. From the SEM images of caviar substitutes, it is logical to infer that addition of OE prior to the formation of the three-dimensional polymer matrix favored the 449
LWT - Food Science and Technology 108 (2019) 446–455
P.K. Binsi, et al.
asymmetric stretching vibration of C–H of CH3 and CH2 groups was not detectable in CS samples. This was also associated with the disappearance of absorption at 1590 cm−1, 1459 cm−1 and 1502 cm−1 in OE containing samples. A much prominent band at 1618 cm−1 and 1869 cm−1 in OE corresponding to carboxylate and five-membered aromatics, was totally absent in CS-0.5 and CS-1 samples, suggesting a possible modification of hydroxyl groups in the roe components and phenolic moieties in OE. The (-CH) band at 1414 cm−1 from the alginate component in CS remained almost unaltered in CS samples, however, the (C-O-C) band at 1033 cm−1 showed a shift to a higher wavelength of 1044 in CS-0.5. Coincidentally, a well-defined ester group was detectable at 1744 cm−1 in CS-0.5 sample which was not detectable in CS-1 and CS samples, which might have resulted from the interaction of terminal carboxyl group of alginate with phenolic components in OE. Generally, if COO- groups are involved in H-bonding a significant band broadening coupled with large shift to lower frequency is expected. However, in the case of essential oils, which contains volatile components, steric hindrance effect may be expected and the band may be observed at natural or higher frequencies (Coates, 2000). Previously, differing opinions about alginate-protein-polyphenol interactions were reported in literature (Chan Yim, Phan, Mansa, & Ravindra, 2010; Nadavala, Swayampakula, Boddu, & Abburi, 2009). In the present study, the alterations observed in the FT-IR profile of caviar samples suggest possible non-covalent interactions of OE with both alginate and roe components.
Table 1 Proximate composition and physico-chemical properties of caviar substitutes. Parameters
Mean Value CS
Moisture (g/100g) Protein (g/100g) Lipid (g/100g) Carbohydrate (g/100g) Ash (g/100g) Physico-chemical properties Yield (%) Tailing percentage (%) Weight average diameter (mm/g) Number average weight (g/ CS**) Bulk density (g/ml) Swelling index (%)
CS-0.5 a
a
CS-1
63.97 ± 0.43 15.43a ± 0.58 2.34a ± 0.71 12.32a ± 0.54 4.61a ± 0.12
61.82 ± 0.75 14.86 a ± 0.54 2.88a ± 0.62 11.53b ± 0.37 4.54a ± 0.23
61.07a ± 0.54 14.73 a ± 0.46 3.18a ± 0.52 11.17b ± 0.18 4.58a ± 0.18
79.70a ± 0.48 0 ± 0.02a 40.24a ± 2.51
82.39b ± 0.39 1.21b ± 0.05 38.73b ± 2.10
75.48c ± 0.81 1.42c ± 0.04 35.00c ± 3.48
0.17a ± 0.04
0.16a ± 0.01
0.18a ± 0.02
0.33a ± 0.08 48.27a ± 0.86
0.38b ± 0.06 60.78b ± 1.17
0.47c ± 0.02 26.25c ± 0.68
*Treatment mean values with same letters are not significantly different from each other (p < 0.05). **CS: Caviar substitute.
formation of beads with homogenous interconnected pores at 0.5% level. The presence of OE maintained the shape of the pores by imparting required hydrophobicity to the gel matrix and repulsion between the micelles and the carboxylate groups of the polymer chain. The results of SEM images further suggests the possibility of higher water entrapment in CS-0.5 as also confirmed by higher yield values of CS-0.5.
3.2.4. Differential scanning colorimetry (DSC) The thermal profile of caviar substitutes were analyzed by an initial cooling phase from 30 to −20 °C followed by a heating phase upto 260 °C above which the material started charring. In general, the thermograms showed a marginal shift in the thermal transition points (Fig. 2). Addition of OE resulted in the depression of freezing point of caviar substitutes from −19.5 °C peak temperature to −17.5 and −15.5 °C in CS-0.5 and CS-1, respectively. The heating curve indicated two distinct endothermic transitions corresponding to melting and denaturation of caviar components. The thermogram indicated slight reduction in peak temperature in CS-0.5 compared to CS, however almost double the value was shown by CS-1 sample. The second transition was comparatively a broader peak in all the samples, which might be a combined peak of volatile components in OE and moisture. Accordingly, the CS sample showed the onset temperature close to the boiling point of water, whereas OE containing samples showed lower values of 64.42 and 78.31 °C respectively, in CS-0.5 and CS-1 samples, respectively corresponding to the volatilization of OE components. The shift in transitional temperature coupled with significantly higher enthalpy of transition suggest the possible structural alterations occurred by the addition of OE in the casting mixture.
3.2.3. Fourier transform-infra red profile (FT-IR) The inclusion of OE markedly altered the FT-IR profile of caviar samples. The spectral behavior in the wavelength range of 3600–1400 cm−1 was analyzed in detail as it represents the characteristic stretching and bending vibrations of OH, COO-and NH groups that primarily contribute to protein-carbohydrate/protein-polyphenol/ carbohydrate-polyphenol interactions through hydrogen bonding. The FT-IR spectra showed the characteristic peaks of roe proteins at 1508 cm−1 and 1607 cm−1, respectively corresponding to the amide Ι (mainly C=O stretch) and II (C–N stretching coupled with N–H bending modes) peaks (Fig. 1E). The position of these peaks remained unaltered with the addition of OE, however, the amide II band was more prominent in OE incorporated samples, which otherwise showed lower peak intensity compared to amide-I in CS sample. This indicates the generation of more side-chain electrostatic interactions, more likely through hydrogen bonding, with the addition of OE. Generally, sodium alginate exhibits significant carbonyl stretching vibration at 1635 cm−1 corresponding to the carboxylate groups in the polymer (Saarai, Kasparkova, Sedlacek, & Saha, 2013). However, this band was appeared as a minor band with major shift towards the higher bandwidth of 1045 cm−1 in control and almost disappeared in OE containing samples, indicating the possibility of utilization of these moieties during the gelation process. Similarly, the major peak observed at 1717 cm−1 in OE corresponding to the carboxylic acid group was totally absent in CS0.5 whereas a less prominent peak was observed in CS-1 sample. These observations suggest the possible interactions of carboxylic group in OE with alginate or/and roe components. The amide A and B bands were not well differentiated in all the caviar samples. However, a band at 2967 was evident in CC which underwent slight shift towards the lower band width in CS samples. This suggests the possible interaction between roe protein and alginate in the caviar samples. The absorption in the broad wavelength range of 3200–3550 cm−1 observed in OE and CS, corresponding to the normal polymeric OH stretch and H-bonded OH stretch, was much condensed in OE containing samples, particularly in CS-1 (Fig. 1F). Similarly, the prominent absorption found in OE in the region of 2870–2970 cm−1 corresponding to the symmetric and
3.2.5. Thermogravimetric/differential thermal analysis (TGA/DTA) The thermal degradation profile of caviar substitutes could not be completely evolved by DSC in the given temperature range due to the interference from moisture as well as charring of the sample at higher temperatures. Hence, simultaneous TGA/DTA was carried out to evolve the degradation pattern of roe-alginate-polyphenol matrix of caviar substitutes. Generally, the thermal decomposition of polysaccharides is characterized by three transitional stages, viz. desorption of physically absorbed water, removal of structural water (dehydration reactions), depolymerisation accompanied by the rupture of C–O and C–C bonds in the ring units that cause the evolution of CO, CO2 and H2O, and finally the formation of polynuclear aromatic and graphitic carbon structures. The thermal analysis profile of both control and OE containing samples indicated four distinct regions of decompositional weight loss (Fig. 3). The initial weight loss observed below 200 °C range might be attributed mainly to the dehydration of the polymer network as this was also observed in polyphenol-free beads. The second major region of weight loss occurred at around 220 °C corresponds to the release of 450
LWT - Food Science and Technology 108 (2019) 446–455
P.K. Binsi, et al.
Fig. 2. A-F. DSC profile of caviar substitutes.
cooking or boiling temperatures, in all the caviar samples. The lower temperatures of decomposition observed for CS-1 in all the transition peaks might be indicative of the formation of a poor gel network in CS1. It should be mentioned that no separate transition peak corresponding to OE was visible in OE containing samples. This further implies that the added OE interacted with roe and alginate components to a greater extent, as also inferred from the FT-IR profile.
decomposition of shorter peptides in the fish roe as well as the polyphenols in oregano extract. Accordingly, highest peak intensity (maximum weight loss) was observed in CS-1 and was much condensed in control CS sample. The higher weight loss observed in OE containing sample in the first transition suggest the loss of unreacted OE as well, as the weight loss was more in CS-1 sample. The third transition point observed at around 280 °C in the DTA curve might be due to the decomposition of roe-alginate network and pure alginate components forming carbonaceous materials. Consequent to this a fourth stage of weight loss appeared in the thermogram at around 320–330 °C due to the loss of carbonaceous material from the sample. In general, The CS and CS-0.5 samples showed similar pattern of decomposition, whereas the CS-1 showed higher rate of decomposition with slightly lower volatilization temperature at all transition peaks. However, the thermograms confirmed the stability and availability of caviar constituents at
3.2.6. Dimensional properties of reconstituted caviar The dimensional properties of set caviars are important as it also indicates the extent of firming, compactness and the size uniformity of the beads. Addition of OE resulted in a slight reduction in the weight average diameter (mm/g) of OE containing caviar, whereas the average unit weight showed slightly higher value for CS-1 (Table 1). The reduction in the average diameter coupled with the increase in the 451
LWT - Food Science and Technology 108 (2019) 446–455
P.K. Binsi, et al.
Fig. 3. A-C. TGA/DTA profile of caviar substitutes.
average weight in OE samples indicates the formation of a compact network with minimum entrapment of water in OE containing samples owing to the hydrophobicity offered by OE, as also revealed from the SEM images.
3.2.7. Bulk density The bulk density values of caviar substitutes were significantly increased (p < 0.05) by the incorporation of OE in the casting solution (Table 1). This might be due to the significant reduction in the average dimension of the caviar beads owing to the formation of more compact matrix. The significantly higher bulk density observed in CS-1 samples 452
LWT - Food Science and Technology 108 (2019) 446–455
P.K. Binsi, et al.
indicates a more or less solid internal structure with minimum porosity as also confirmed by SEM images.
increases with a reduction in pH of the food, since at low pH the hydrophobicity of the oil increases, enabling it to more easily dissolve in the lipids of cell membrane of the target bacteria (Burt, 2004). Previously (Lin, Labbe, & Shetty, 2004), a marginal inhibitory effect was reported on Listeria monocytogenes in beef and fish slices in presence of oregano and cranberry extract even after 18 h at pH 7, whereas significant differences in viable cell counts were observed at pH 6.0. In the present study, in both the treated samples, pH remained below or almost equal to 6 till the end of chilled storage, whereas that of control CS crossed 6 after 16th day.
3.2.8. Swelling index The diameter of the caviar before and after suspending in aqueous media was evaluated to assess any dimensional alterations. Both control and OE added samples retained the integrity in aqueous media even after dipping for 30 min. However, distinct difference in the diameter of the beads were observed, with a significant extent of swelling in CS-0.5 whereas CS-1 showed a much lower value compared to control CS samples (Table 1). This might be due to the formation of regular porous internal structure of CS-0.5 congenial for better diffusion and entrapment of water molecules, compared to the random plated structure of CS-1. The results of dimensional properties are also in agreement with the structural features derived from SEM, FT-IR and thermal analysis.
3.3.2. Total volatile base - nitrogen (TVB-N) The mean TVB-N values of caviar samples during chilled storage period indicated significant difference between the control and OE treated samples (p < 0.05) (Fig. 4B). Treatment with OE was found to be more effective in delaying TVB-N formation during chilled storage, which may be attributed to the antimicrobial property of the phenolic constituents in oregano extract as observed in our previous study (Binsi et al., 2016). The mean TVB-N values of caviar samples over the period of chilled storage indicated significantly lower mean values for OE treated samples (p < 0.05). The TVB-N values increased rapidly after 4th day of chilled storage in control caviar samples, whereas OE treated samples showed minimum generation of volatile base nitrogen compounds (VB-N) throughout the chilled storage period.
3.3. Changes during chilled storage 3.3.1. pH pH values showed increasing trend throughout the storage period, with lower absolute values for samples containing OE as compared to control (Fig. 4A). As storage period progressed, pH of control sampleincreased by more than 1 pH unit, whereas in CS-0.5 and CS-1, an increase of only 0.23 and 0.25 units respectively was observed. This might be attributed to the antibacterial properties of oregano extract which retarded the decomposition of protein substrate into amino acids and short peptides. The bacterial susceptibility to essential oils
3.3.3. Lipid oxidation indices The PV rose sharply during the initial 7 days of storage in control Fig. 4. A-F. Changes in (A) pH (B) TVB-N (C) PV (D) TBARS (E) TVC (F) Enterobacteriaceae count of caviar substitutes.
453
LWT - Food Science and Technology 108 (2019) 446–455
P.K. Binsi, et al.
samples, with a peak value on 8th day of chilled storage (p < 0.05) (Fig. 4C). A slower increase in PV was observed in OE treated samples, demonstrating the higher oxidative stability of roe lipids during chilled storage in the presence of OE. Generally, peroxide value between 5 and 10 mEq/kg indicates the commencement of rancidity. In the present study, CS sample crossed 5 mEq/kg on 4th day of storage, whereas PV of OE treated samples were well below the limit throughout the storage period. The TBARS values of CS sample crossed the limit of 2 mg of MDA/kg (Connel, 1995, p. 241), after 4th day of storage indicating the onset of oxidative rancidity (Fig. 5D). In OE treated samples, TBARS values followed almost similar pattern at both the concentrations, and remained well below this range throughout the storage period. The protective effect of oregano essential oil, mint leaf extract and essential oils of clove and curry leaf on chill stored fish and fish oil encapsulates by minimizing the generation of peroxy free radicals was demonstrated in our previous studies (Binsi et al., 2016, 2017a; Jeyakumari, Zynudheen, Binsi, Parvathy, & Ravishankar, 2017; Viji et al., 2016). In the present study, the protective effect was evident at a lower concentration of 0.5% and doubling the concentration further did not contribute significantly (p < 0.05) to the protective mechanism.
log cfu/g till the end of the study (Fig. 4E). On the contrary, CS-1 samples indicated less than a unit log increase in TVC till the end of storage period, which might be related to the higher content of free essential oil in the caviar matrix. Zinoviadou, Koutsoumanis, and Biliaderis (2009) reported that 1.5% oregano essential oil incorporated whey protein isolate edible films resulted in 3.3 log reduction of TVC on fresh beef cuts as compared to the control sample on 8th day of refrigerated storage. In the present study, the control samples were rejected on 27th day of chilled storage, whereas preservative effect was observed even at 0.5% level eventhough 1% OE had a better protective effect. Enterobacteriaceae and E. coli counts are often used to assess the overall hygiene status of the processing operations and the temperature history of the product during storage. In the present study, Enterobacteriaceae was not detectable in OE treated samples, however it was present in control caviar samples (Fig. 4F). Escherichia coli was not detected in any of the samples throughout the chilled storage period, indicating that the roe was not contaminated with gut content of fish during gutting and cleaning steps. Apart from that, this also indicates the best management practices followed in the aquaculture farm.
3.3.4. Microbiological parameters During chilled storage, bacterial growth progressed much faster in control caviar samples compared to OE treated samples, as indicated by the higher microbial count in CS from 1st day of storage onwards (Fig. 4E & F). TVC of CS-0.5 samples showed a progressive increase during the storage period, however, the count remained well below 4
3.3.5. Texture profile analysis (TPA) The texture profile values indicated only marginal variation between the samples during initial period of chilled storage (Fig. 5). The fresh samples of caviar substitutes showed almost similar hardness values, whereas a slight hardening effect was observed in OE samples Fig. 5. A-F. Changes in TPA profile of caviar substitutes.
454
LWT - Food Science and Technology 108 (2019) 446–455
P.K. Binsi, et al.
on the third day of chilled storage. Among the samples, slightly lower hardness value was observed for CS-1 samples initially, probably because of the higher content of OE, which might have interfered with the roe-alginate network formation. However, the value increased during subsequent days of storage similar to CS-0.5 sample. The control sample showed a progressive reduction in the hardness values during the storage period, whereas that of OE samples remained almost stable till the end of the study. The hardness-2 values showed distinct differences between the samples after 1st day of storage, with significantly lower values for control samples. This implies the matrix stabilizing effect of OE, by way of structural modification. Similar changes were observed in all the other parameters, with higher springiness, chewiness, cohesiveness and stiffness values for OE treated samples, particularly during the latter period of storage. The changes in the texture profile of caviar substitutes further confirms the structure stabilization effect of OE via protein/alginate–polyphenol interactions. However, only marginal difference was observed between CS-0.5 and CS-1 samples during chilled storage.
doi.org/10.1016/j.lwt.2019.03.001. References AOAC (2000). Official methods of analysis of association of official analytical chemists international, 17th, suite 500,481,North frederick avenue, Gaithersburg, Maryland 208772417, USA. Becker, T. A., Kipke, D. R., & Brandon, T. (2001). Calcium alginate gel: A biocompatible and mechanically stable polymer for endovascular embolization. Journal of Biomedical Materials Research Part A, 54(1), 76–86. Binsi, P. K., Natasha, N., Sarkar, P. C., Ashraf, P. M., George, N., & Ravishankar, C. N. (2017). Structural, functional and in vitro digestion characteristics of spray dried fish roe powder stabilised with gum Arabic. Food Chemistry, 221, 1698–1708. Binsi, P. K., Nayak, N., Sarkar, P. C., Jeyakumari, A., Muhamed Ashraf, P., Ninan, G., et al. (2017a). Structural and oxidative stabilization of spray dried fish oil microencapsulates with gum Arabic and sage polyphenols: Characterization and release kinetics. Food Chemistry, 219, 158–168. Binsi, P. K., Ninan, G., & Ravishankar, C. N. (2017b). Effect of curry leaf and clove bud essential oils on textural and oxidative stability of chill stored sutchi catfish fillets. Journal of Texture Studies, 48(3), 258–266. Binsi, P. K., Ninan, G., Zynudheen, A. A., Neethu, R., Ronda, V., & Ravishankar, C. N. (2014). Compositional and chill storage characteristics of microwave‐blanched sutchi catfish (Pangasianodon hypophthalmus) fillets. International Journal of Food Science and Technology, 49(2), 364–372. Binsi, P. K., Ravishankar, C. N., Mathew, S. S., Athira, V. P., Biji, K. B., Joshy, C. G., et al. (2016). Comparative evaluation of natural antioxidant coating and vacuum-packaging technique on quality characteristics of chill stored giant trevally fillets. Journal of Aquatic Food Product Technology, 25(2), 197–209. Binsi, P. K., Viji, P., Panda, S. K., Mathew, S., Zynudheen, A. A., & Ravishankar, C. N. (2016a). Characterisation of hydrolysates prepared from engraved catfish (Nemapteryx caelata) roe by serial hydrolysis. Journal of Food Science and Technology, 53(1), 158–170. Burt, S. (2004). Essential oils: their antibacterial properties and potential applications in foods—a review. International Journal of Food Microbiology, 94(3), 223–253. Chan, E. S., Yim, Z. H., Phan, S. H., Mansa, R. F., & Ravindra, P. (2010). Encapsulation of herbal aqueous extract through absorption with ca-alginate hydrogel beads. Food and Bioproducts Processing, 88(2), 195–201. Coates, J. (2000). Interpretation of infrared spectra, a practical approach. Encyclopedia of analytical chemistry. Connel, J. J. (1995). Control of fish quality. Cambridge, London: Fishing New Books. Blackwell Science Ltd. Conway, E. J. (1950). Micro-diffusion analysis and volumetric error. Crosby. London: Lockwood and Son Ltd. Daemi, H., & Barikani, M. (2012). Synthesis and characterization of calcium alginate nanoparticles, sodium homopolymannuronate salt and its calcium nanoparticles. Scientia Iranica, 19, 2023–2028. Jeyakumari, A., Zynudheen, A. A., Binsi, P. K., Parvathy, U., & Ravishankar, C. N. (2017). Microencapsulation of fish oil-oregano essential oil blends by spray drying and its oxidative stability. Journal of Agricultural Science and Technology A, 19, 1539–1550. Klokk, T. I., & Melvik, J. E. (2002). Controlling the size of alginate gel beads by use of a high electrostatic potential. Journal of Microencapsulation, 19, 415–424. Lin, Y. T., Labbe, R. G., & Shetty, K. (2004). Inhibition of Listeria monocytogenes in fish and meat systems by use of oregano and cranberry phytochemical synergies. Applied and Environmental Microbiology, 70(9), 5672–5678. Nadavala, S. K., Swayampakula, K., Boddu, V. M., & Abburi, K. (2009). Biosorption of phenol and o-chlorophenol from aqueous solutions on to chitosan–calcium alginate blended beads. Journal of Hazardous Materials, 162(1), 482–489. Saarai, A., Kasparkova, V., Sedlacek, T., & Sáha, P. (2013). On the development and characterisation of crosslinked sodium alginate/gelatine hydrogels. Journal of the Mechanical Behavior of Biomedical Materials, 18, 152–166. Stojanovic, R., Belscak‐Cvitanovic, A., Manojlovic, V., Komes, D., Nedovic, V., & Bugarski, B. (2012). Encapsulation of thyme (Thymus serpyllum L.) aqueous extract in calcium alginate beads. Journal of the Science of Food and Agriculture, 92(3), 685–696. Tarladgis, B. G., Watts, B. M., Younathan, M. T., & Dugan, L. (1960). A distillation method for quantitative determination of malonaldehyde in rancid foods. Journal of the American Oil Chemists’ Society, 37, 44–48. Viji, P., Binsi, P. K., Visnuvinayagam, S., Bindu, J., Ravishankar, C. N., & Gopal, T. K. S. (2015). Efficacy of mint (Mentha arvensis) leaf and citrus (Citrus aurantium) peel extracts as natural preservatives for shelf life extension of chill stored Indian mackerel. Journal of Food Science and Technology, 52(10), 6278–6289. Viji, P., Binsi, P. K., Visnuvinayagam, S., Ravishankar, C. N., Venkateshwarlu, G., & Gopal, T. K. S. (2016). Modified icing system containing mint leaf and citrus peel extracts: Effects on quality changes and shelf life of Indian mackerel. Indian Journal of Fisheries, 63(2), 93–101. Yildiz, G., Wehling, R. L., & Cuppett, S. L. (2003). Comparison of four analytical methods for the determination of peroxide value in oxidized soybean oils. Journal of the American Oil Chemists’ Society, 80, 103–107. Zinoviadou, K. G., Koutsoumanis, K. P., & Biliaderis, C. G. (2009). Physico-chemical properties of whey protein isolate films containing oregano oil and their antimicrobial action against spoilage flora of fresh beef. Meat Science, 82(3), 338–345.
3.3.6. Sensory evaluation of caviar substitutes The sensory acceptability is an important parameter for evaluating the quality of caviar substitute as there exist well defined grading systems for caviar and caviar related products, which is even specific to the individual fish species in the International market. However, as there is no standard specifications for carp caviar (as it originally exist as gelly like mass), the general descriptions for scoring caviar products was followed. Accordingly, higher sensory score was obtained for CS-0.5 followed by CS (Fig. S1). The CS-1 scored less in particular for texture compared to other two samples. The CS-0.5 presented soft and spongy texture, whereas control CS samples presented grittiness towards the core. Apart from that control samples exhibited stickiness posing difficulty in mastication. The CS-1 samples were less spongy and hard in texture, presenting uneasiness while chewing. Moreover, the flavor of oregano was more predominant in CS-1 samples, and scored less for flavor attribute. 4. Conclusion The chilled storage stability of caviar substitute prepared from carp roe mass was evaluated. Addition of oregano extract at 0.5% improved the textural and sensory properties of caviar substitutes. Further, the addition of oregano extract improved the chilled storage stability of caviar substitutes in terms of oxidative and microbial parameters. A possible correlation between the polyphenol-roe-alginate interaction and textural stabilization was derived. The current study identifies the potential of utilizing carp roe by converting to novel high value products such as fish caviars with suitable stabilizers such as plant polyphenols. Conflicts of interest The authors have no conflicts of interest to declare. Acknowledgement This work was carried out under the research project jointly supported by Science and Engineering Research Board SERB (Department of Science and Technology, India) and MOFPI (Ministry of Food Processing Industries, India). Appendix A. Supplementary data Supplementary data to this article can be found online at https://
455