Optimization of pretreatment and evaluation of quality of jackfruit (Artocarpus heterophyllus) bulb crisps developed using combination drying

Accepted Manuscript Title: Optimization of pretreatment and evaluation of quality of jackfruit (Artocarpus heterophyllus) bulb crisps developed using combination drying Author: Alok Saxena Tanushree Maity P.S. Raju A.S. Bawa PII: DOI: Reference:

S0960-3085(15)00055-3 http://dx.doi.org/doi:10.1016/j.fbp.2015.04.005 FBP 600

To appear in:

Food and Bioproducts Processing

Received date: Revised date: Accepted date:

15-7-2014 8-4-2015 16-4-2015

Please cite this article as: Saxena, A., Maity, T., Raju, P.S., Bawa, A.S.,Optimization of pretreatment and evaluation of quality of jackfruit (Artocarpus heterophyllus) bulb crisps developed using combination drying, Food and Bioproducts Processing (2015), http://dx.doi.org/10.1016/j.fbp.2015.04.005 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

RESEARCH HIGHLIGHTS  Effect of combination-drying on quality of pretreated jackfruit bulb crisp was evaluated.  Pretreatment variables were optimized using response surface methodology

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 Quality of crisps was found to be affected by various freeze and hot air drying combinations

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 SEM micrograph showed restricted shrinkage in case of optimized combination drying protocol

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Optimization of pretreatment and evaluation of quality of jackfruit (Artocarpus heterophyllus) bulb crisps developed using combination drying

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Amity Institute of Food Technology, Amity University, Noida 210313, Uttar Pradesh, India b

Defence Food Research Laboratory, Siddarthanagar, Mysore-570011, Karnataka, India

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*Corresponding author E-mail address: [email protected] (A. Saxena)

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Alok Saxena a,*, Tanushree Maity b, P.S. Raju b, A.S. Bawa a

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Nomenclature Total color difference

AT

Ambient temperature

BSC

Blanching solution concentration

BT

Blanching time

CD

Combination drying

FD

Freeze drying

HAD

Hot air drying

OAA

Over all acceptability

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∆E

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Abstract The effects of pre-treatments and a combination of freeze drying (FD) and hot airdrying (HAD) were investigated to optimize the processing conditions for the development of jackfruit (Artocarpus heterophyllus L.) bulb crisps. Response surface methodology (Box-

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Behnken design) was used to optimize independent pre-treatment variables such as calcium salt infusion, and osmo-blanching process parameters with respect to the crispness, visual

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color (Hunter L × b value), and overall acceptability scores of the freeze-dried crisps. The

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optimized conditions of pre-treatments were found to be 1.38 % w/v CaCl2, 28.2 °brix blanching solution, and 5.2 min. blanching time. The optimized pre-treatments were applied

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to other modes of drying such as HAD and various combination-drying (CD) schedules involving a decrease in FD phase followed by an increase in HAD phase. The dried crisp

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product obtained from various drying schedules was evaluated for rehydration characteristics, shrinkage, textural properties, color values, and overall acceptability. The extent of shrinkage

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was 8 to 50 % in case of FD and HAD procedures respectively. The optimized CD protocol

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resulted in a product comparable in quality to the freeze-dried samples. The combination-

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dried jackfruit bulbs have a potential for commercialization because of the product quality being equivalent to freeze-dried ones. Keywords: Jackfruit bulbs; Freeze-drying; Combination-drying; Rehydration; Shrinkage; Microstructure

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1. Introduction Jackfruit (Artocarpus heterophyllus L.) is a tropical composite fruit having golden yellowish bulbs. The fleshy pericarp is rich in sugars, minerals, carboxylic acids, dietary fiber, and vitamins such as ascorbic acid, and thiamine (Rahman et al., 1999). However, the

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fruit is highly perishable, once it ripens, and the spoilage is usually localized in certain pockets of the giant fruit. Certain value added products in the form of high moisture and

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intermediate moisture products have been developed from jackfruit such as minimally

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processed bulbs (Saxena et al., 2013, Saxena et al., 2012), multi-target approach preserved bulbs (Saxena et al., 2009), canned juice (Seow, & Shanmugam, 1992), fruit leather (Man &

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Sin, 1997), blast and cryo-frozen bulbs (John, & Narasimham, 1998) and fruit bars (Manimegalai et al., 2001). However, the information on dehydrated products form jackfruit

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bulbs is scanty and needs attention to realize its commercial potential. Drying is a popular technique used for fruits and vegetables due to reduction in bulk,

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low packaging and transportation costs besides being microbially safe, and shelf-stable.

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However, the quality of the dried products needs to be very good as improper drying could be

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detrimental to product quality in terms of texture, color, nutritive value, and rehydration characteristics (Nijhuis et al., 1998). Conventional hot air-drying is the most economical of all the drying techniques. However, product quality as affected by case hardening and shrinkage needs to be addressed through pre-treatments like infusion of texturizing additives (Jayaraman et al., 1990). Freeze-drying has been extensively reported to be an ideal method due to minimal shrinkage resulting in a porous product with excellent rehydration characteristics, while the low temperatures used ensures maximum retention of nutrients (Ratti, 2001). However, since freeze-drying is highly energy intensive and a costly process, a judicious combination with other drying methods such as hot air drying, vacuum drying, microwave vacuum drying and osmotic drying has been recommended (Jiang et al., 2014; Pei

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et al., 2014; Fernandes et al., 2008; Contreras et al., 2005; Phanindrakumar et al., 2001; Schadle et al., 1983). Drying of fruits involves several physico-chemical changes, including water activity (aw) and mobility of solutes such as sugars. These aspects in turn define the quality of the

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dehydrated product in terms of features such as case hardening (Krokida et al., 2000). Pretreatments such as calcium infusion into the plant tissue have been reported to maintain the

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surface area and better texture in case of rehydrated apples, potatoes and tomatoes (Ahrne et

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al., 2003; Pani et al., 2008). Osmo-blanching could also impose a minor osmotic drying effect in the tissue and prevent enzymatic browning. Response surface methodology (RSM)

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could be used as a statistical technique for optimization of processing conditions for a variety of food processes (Torreggiani et al., 1995; Fan et al., 2005; Fernandes et al., 2006). It is an

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effective tool to study the interaction between the processing variables, as well as modeling and analysis of concerned response of interest. Use of RSM facilitates reduction in number of

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factorial designs.

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experimental runs and provides useful information with statistically valid results than full

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The objective of the current study was to optimize the pre-treatments consisting of Ca salt infusion and osmo-blanching variables such as blanching solution concentration, and blanching time for drying of jackfruit bulb slices. The quality of the crisps obtained through freeze-drying and hot air-drying or various combinations thereof was evaluated with respect to textural aspects, sensory quality and shelf-stability in terms of physico-chemical and sensory attributes.

2. Materials and Methods 2.1 Sample preparation 500 kg of a local jackfruit cultivar (firm variety), with an average weight of 8-10 kg per piece and brownish yellow skin color at the uniform ripening stage evidenced by wide gaps between the spikes, without any physical blemishes or malformations was procured for

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the study from the local fruit market at Mysore, India and the entire study was conducted at Fruits and Vegetables Technology department of Defence Food Research Laboratory, Mysore India. Jackfruits were surface sanitized with 100 ppm chlorinated water. Those with mechanical bruises and visible microbial infections were sorted out. Manual cutting along the

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axis using sharp edged stainless steel (SS) knives was used to open the fruits. Edible bulbs were removed from the rind and the seeds separated by vertical slitting. The yield of pitted

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bulbs was found to be 35%. The bulbs were manually cut into slices having dimensions of 6

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cm length × 3 cm width × 0.5 cm thickness using SS knives. Jackfruit bulb slices were given a secondary phyto-sanitation wash in chilled chlorinated (35-ppm) water for 5 min. About

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175 kg pre-cut and pitted bulbs were used to study the different aspects including optimization of the pre-treatment, dehydration schedules as well as shelf-stability.

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2.2 Pre-treatment

Before subjecting the pre-cut fruits to drying, the pre-treatments were applied to

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reduce browning and other quality related changes. RSM (Box-Behnken design) with three

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independent variables at three levels each were used to optimize the pre-treatment conditions.

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The experimental variables included blanching solution concentration (10-30 °brix) for osmoblanching, blanching time (2-6 min) and CaCl2 concentration (0.5-1.5 % w/v). The range and central point values of the independent variables (Table 1) were determined based on preliminary experiments. The concentrations of the blanching solutions were determined using a hand refractometer (Atago Co. Ltd, Tokyo, Japan). Seventeen sets of experiments were carried out at three levels of each variable. The different batches of surface sanitized jackfruit bulb slices were subjected to osmo-blanching in different sugar syrups at 85 °C using food grade commercial cane sugar for varying durations in compliance with the experimental format (Table 2). The blanching solutions contained 0.3% (w/v) citric acid and 1% (w/v) potassium metabisulfite. The blanched samples were dipped in water containing defined % (w/v) of CaCl2 as per the experimental format for 30 min under ambient

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temperature conditions with fruit: solution ratio of 1:2 (w/v). Drained slices were subjected to freeze-drying conditions. The pre-treatments were optimized to determine the levels of independent variables, such as blanching solution concentration (BSC), blanching time (BT), and CaCl2 concentration. The responses studied were maximum crispness and overall

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acceptability scores and visual color (Hunter L × Hunter b value) change. The optimized values of the experimental variables for freeze-dried crisps were also used in the case of other

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drying experiments such as hot air-drying and combination-drying. Out of the various drying

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experiments, a combination-drying protocol yielding crisps with acceptable sensory quality was further evaluated for rehydration ratio, shrinkage, textural changes, color values, micro-

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structure and sensory characteristics during storage under ambient temperature (22-32 ºC), as well as 37 ºC conditions.

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2.3 Optimization

Response data was fitted into the second-order polynomial model (eq.1), which

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response Y.

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described the effect of test variables, their interactions and the combined effect on the

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Yi = ß0 + ß1X1 + ß2X2 + ß3X3 + ß12 X1X2 + ß13X1X3 + ß23X2X3 + ß11X12 + ß22X22+ ß33X32 … (1) where Y is the predicted response, ßo the estimated regression coefficient of the fitted

response at the center point of the design, ß1, ß2, ß3 the regression coefficient for linear effect terms, ß11, ß22, ß33 the quadratic effects and ß12, ß13, ß23 the interaction effects. Model analysis and lack-of-fit tests were carried out to determine the adequacy of the polynomial models and significance of the model was determined using analysis of variance at P < 0.05. A good fit of a model was considered when coefficient of determination (R2) was more than 0.8. Replication of the center point has been found to be useful in conducting a formal test for lack of fit on the regression model (Myers & Montgomery, 2002). Non-significant (P > 0.05) effects were eliminated from initial equation without damaging the model hierarchy and finally the reduced equation was obtained by refitting the experimental data only with

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statistically significant parameters (P < 0.05). A graphical optimization technique was used by fixing one of the variables at a pre-determined optimum level and superimposing the contour plots of the various response variables in order to find workable optimum conditions. Numerical optimization was carried out by defining constraint criterion at maximum and

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minimum ranges of the responses to determine the exact optimum level of independent variables. The experimental design matrix, data analyses and optimization procedure were

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generated using commercial statistical package, Design-Expert version 7.1.5 (Statease Inc.,

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Minneapolis, USA, Trial version). All results were expressed as the average values of three independent trials.

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2.4 Drying 2.4.1 Freeze-drying

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The samples were pre-frozen in a blast freezer at -30 °C for 3-4 h in SS sample holding trays (loading density 3.52 kg/ m2) and freeze-dried in a pilot scale freeze drier

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Epsilon 1/60 (Martin Christ GmbH & Co KG, Osterode, Germany), to a moisture level of 4-

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6%. Dehydration was carried out by maintaining the chamber pressure at 100-300 Pa and

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plate temperature at 50 °C for a period of 20 hrs. At an interval of 2 h, the weight of sample was recorded to determine moisture removal and drying kinetics. The weight loss was measured using a weigh cell installed under the sample holding tray and connected to a registering device to record the data. The dried samples were placed in desiccators overnight to equilibrate the moisture and subsequently packed in paper-foil-polyethylene, (PFP) pouches (paper-42 gsm, Al foil-0.012 mm, polyethylene-150 gauge) and kept in a low relative humidity atmosphere (23 ± 2 %) chamber to avoid absorbance of moisture by the samples. 2.4.2 Hot air-drying The samples were spread on drying trays in a single layer (loading capacity 5.9 kg/ m2) and hot-air dried in a Kilburn crossflow cabinet hot-air dryer set at 60 °C with 2 m s-1 air

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velocity. At an interval of 2 h, the samples were drawn for determination of moisture removal and drying kinetics. Samples were dehydrated to a moisture level of 5-7 %. 2.4.3 Combination-dehydration A combination-dehydration process consisting of freeze-drying followed by hot air-

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drying was carried out. Different trials consisted of a decrease in the freeze-drying phase (i.e. 10, 8, 6, 4 h) followed by increase in the hot air-drying phase (i.e. 2, 4, 6, 8, 10, 12 h). The

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moisture content of the samples was determined as described earlier and the drying was

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carried out to obtain a final moisture content of 5-7 %. Final products from different combination-drying schedules were packed in PFP pouches (100g unit-1).

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All the drying experiments were replicated three times and the average values reported.

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2.5 Shrinkage

Shrinkage observed in term of volume reduction in dried crisps was evaluated by n-

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heptane (S.D. Fine chemicals Ltd., Mumbai, India) displacement method (Krokida et al.,

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1998). Percentage decrease in the crisps volume in relation to its initial volume was

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determined using the following equation: % Shrinkage =

Vo - Vf X 100 …… (2) Vo

where Vo was the volume of initial sample, and Vf volume of the dehydrated sample.

All the measurements were replicated three times and the mean values reported. 2.6 Rehydration ratio

Rehydration ratio of crisps was determined using a rehydration technique as per

Ranganna (1986). 10 g of samples were immersed in 200 ml of sterile water at 80°C for 30 minutes in a beaker. The excess water was soaked off using Whatman No. 4 filter paper. The weight of drained sample was recorded and rehydration ratio calculated using following equation: Rr = Wf …… (3) 35

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Wo where Wo was weight of the dried sample and Wf drained weight of the rehydrated sample. All the measurements were replicated three times and the average values reported. 2.7 Texture analyses

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The textural properties of the dried samples were measured using a texture analyzer (TAHdi; Stable Micro Systems, London, UK). This was equipped with a CFS (crisp fracture

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support) rig with 5 mm dia ball SS ball probe operating at a test speed of 0.5 mm s-1 over a

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distance of 5 mm and was used to break the sample using a load cell of 5 kg. Pre-test and post-test speeds were set at 1 mm s-1 and 5 mm s-1 respectively. The data obtained from

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texture profile analysis were used for determining the hardness and crispness values. Hardness was expressed as maximum force required in the first compression and crispness as

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the force at significant break in the first bite (Fig.1). 2.8 Color measurement

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The color of the jackfruit crisps was measured using a tri-stimulus colorimeter (Model

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2810, Data Lab India Pvt. Ltd., India) under D65 illuminating lamp conditions at an observer angle of 10°, calibrated using a white ceramic tile. The color values were expressed as L-

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(lightness/ darkness), a- (redness/ greenness), and b- (yellowness/ blueness) values on the Hunter scale. The combination of Hunter L×b value was used as a tool to judge the color degradation in jackfruit bulb slices during drying as described earlier (Saxena et al., 2012). From the values of L, a and b, total color difference (∆E) was also calculated as follows. Total color difference (∆E) = [(L - Lo) 2 + (a - ao) 2 + (b - bo)2]1/2…… (4)

where Lo, ao and bo were the color values of either fresh jackfruit bulbs (in case of pre-

treatment optimization) or freeze-dried crisps (in case of comparison of various drying schedules) to determine ∆E of the crisps. 2.9 Sensory evaluation The sensory scores of jackfruit bulb crisps were determined in terms of color, taste, texture, and overall acceptability (OAA) by a panel consisting of ten semi-trained panelists 36

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using a nine point hedonic scale (9: excellent; 7: good; 5: acceptable (limit of marketability); 3: poor and 1: extremely poor) (Larmond, 1977). Samples were randomly drawn from each experimental block, coded, and served to the panelists randomly in a room illuminated with white light and maintained at 25 °C.

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2.10 Microstructure

Microstructural analyses of the samples were carried out using a scanning electron

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microscope (Quanta 400, Environmental SEM, FEI Company, USA) at Defence Research

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and Development Establishment, Gwalior, India. Specimens were prepared by treating with ethanol followed by critical point drying (CPD) using liquid carbon dioxide. The sample

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specimens were mounted on brass stubs using double sided adhesive tapes and gold coated in an ion sputter coating unit (JEOL JFC 1100, Tokyo, Japan) for 10 min under low vacuum

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with argon gas to provide a reflective surface for the electron beam. An accelerating potential

2.11 Shelf-stability

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of 20 kV was used during micrography and images magnified 500 times.

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Out of the various dehydration schedules, a combination-drying protocol having

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acceptable quality attributes of the crisps was further evaluated for shelf-stability under ambient and 37 ºC temperature conditions. Shelf-stability evaluation included periodic determination of moisture content; aw (Aqua Lab water activity meter, Decagon Devices Inc., USA); total carotenoids (Marina et al., 1989); ascorbic acid (AOAC, 1997), textural attributes i.e. hardness and crispness, instrumental color as well as sensory evaluation. 2.12 Statistical analysis

The results obtained from both physico-chemical analyses and sensory evaluation of the dehydrated product using a combination-drying technique during the storage studies were statistically evaluated for significance (P ≤ 0.05) of the treatments using analysis of variance (ANOVA). 3. Results and Discussion

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3.1 Pretreatment The pre-treatments prior to dehydration were optimized in terms of experimental variables such as CaCl2 concentration, blanching solution concentration (BSC), and blanching time (BT) with respect to crispness, visual color (L×b), and OAA scores. The

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various responses under different combinations as described in the experimental design (Table 1 and 2) were evaluated using ANOVA (Table 3). The coefficients for the actual

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functional components, predicting the responses during the optimization process, are given in

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Table 4. The results from Tables 3 & 4 showed that all the responses had significant sum of squares, non-significant lack of fit and high regression coefficients indicating compliance of

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the response profile with the given set of variances in a second order polynomial (Eq. 1). 3.1.1 Effect of processing variables on crispness

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Fig 2a describes the contour plot for ‘CaCl2 conc (%). and BSC (brix)’ with BT (min.) at its central value. It showed that the values of crispness in response to the

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experimental variables varied from 3.06 to 5.09 N. Out of the different variable

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combinations, a combination of 1.5 % CaCl2, 30 brix BSC and 4 min BT gave the highest

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crispness while the lowest was recorded for combination having 0.5 % CaCl2, 10 brix BSC and 4 min BT (Table 2). As shown in Table 4, all the three experimental variables were found to have a significant effect on crispness of the product. Increasing CaCl2 conc. was found to increase the crispness of the samples as indicated by maximum positive regression coefficient compared to other variables such as BSC and BT. This may be due to the fact that a higher % of CaCl2 could lead to the formation of calcium pectate in the fruit tissue resulting in an increased crispness (Ahrne et al., 2003). BSC was found to affect the crispness of dehydrated jackfruit crisps, though at a lower magnitude. However, Deng and Zhao (2008) reported that osmotic pre-treatment was found to be ineffective for crispness of dried apple. Among all the interactions between the various variables, the interaction between CaCl2 conc. and BSC was found to affect the crispness of the product significantly (Fig 2a). Similarly, the significant 38

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(P<0.05) regression coefficients (Table 4) at quadratic levels of BSC and BT indicated significant affect on the crispness of the product. The multiple regression equation in uncoded form showed that the final reduced model given below fitted well for describing the relationship between the process variables and response:

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Crispness (N) = 0.525 + 1.704* X1 + 0.118* X2 + 0.646* X3 - 0.014* X1* X2 - 0.002* X22 0.061* X32…..(5)

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3.1.2 Effect of processing variables on visual color (L×b)

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where, X1: CaCl2 conc (%); X2: Blanch. Sol. Conc. (brix); and X3: Blanch. Time (min.)

Fig 2b describes the contour plot for ‘BT’ and ‘BSC’ with CaCl2 conc. at its central

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value. It showed that the visual color of the crisps in terms of Hunter L×b values varied from 2232.66 to 2503.56. The highest visual color value was observed in the case of 1.5 % CaCl2,

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10 brix BSC and 4 min BT combination and the lowest for a set having the combination 1 % CaCl2, 30 brix BSC and 6 min BT (Table 2). The regression coefficients reported in Table 4

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indicated that BSC followed by BT imparted a significant negative effect on the visual color

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by decreasing the Hunter L×b value while the increasing CaCl2 conc. increased visual color

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by enhancing it. Higher BSC % could cause darkening of the product resulting in lower visual color values. Therefore, it could be deciphered that the visual color is mainly a function of BSC rather than BT and CaCl2 conc. Interaction between the ‘BSC and BT’ gave a significant (P<0.05) negative effect by decreasing the Hunter L×b value whilst other interaction terms showed a non-significant effect on visual color. However, at the quadratic level, BSC had greater and significant (P<0.05) positive effect whilst BT had a significant (P<0.05) negative effect on visual color. The blanching was reported to decrease the L* and a* values and increase the b* value when bamboo shoot slices were subjected to FD and HAD (Zheng et al; 2014). The multiple regression equation in uncoded form showed that final reduced model given below provided a good fit for describing the relationship between the process variables and response: 39

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Visual color (Hunter L×b value) = 81.57 - 0.24X1 - 0.19X2 + 0.44X3 - 0.02X2X3 + 0.002X22 0.04X32…….(6) where, X1: CaCl2 conc (%); X2: Blanch. Sol. Conc. (brix); and X3: Blanch. Time (min.) 3.1.3 Effect of processing variables on overall acceptability scores

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The quality of dehydrated crisp product is largely influenced by textural and color attributes. Fig 2c describes the contour plot for ‘BT’ and ‘CaCl2 conc.’ with BSC at its central

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value. The OAA score varied from 6.6 to 8.4 for different combinations of treatment. Out of

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the different combinations, a set having 1 % CaCl2, 30 brix BSC and 6 min BT gave the highest OAA score while the lowest was recorded for the set having 0.5 % CaCl2, 10 brix

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BSC and 4 min BT combination (Table 2). The regression coefficients in Table 4 indicated a significantly (P<0.05) higher positive effect of BSC in linear terms on OAA score followed

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by CaCl2 conc. and BT. During sensory evaluation, the texture of the crisps was found to be a major factor in deciding its acceptability; this was significantly affected by BSC and CaCl2

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conc. However, all the quadratic terms with CaCl2 conc., at its highest value were found to

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have significant negative effects on OAA scores for the jackfruit crisps. Except interaction

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terms of CaCl2 conc. and BT, all the other interaction terms showed non-significant (P>0.05) effects on the OAA score of jackfruit crisps implying that the interaction between the different treatments did not influence the response. The coefficient of determination R2 had a value of 0.994 indicating a good fit between the quadratic model and the experimental data. The multiple regression equation given below in uncoded form showed that the final reduced model fitted well for describing the relationship between the process variables and response: OAA Score = 7.94 - 1.33X1 - 0.02X2 + 0.22X3 - 0.01X1X2 - 0.02X2X3 + 1.42X12 + 0.002X22…....(7) where, X1: CaCl2 conc (%); X2: Blanch. Sol. Conc. (brix); and X3: Blanch. Time (min.) 3.1.4 Optimization

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Numerical and graphical optimization techniques were adopted to optimize the different pre-treatment variables for the dehydration of jackfruit bulbs. For any two given sets of variables, the third one was kept constant and overlaid contours were created between the other two variables. Fig 3a describes the overlay plot for CaCl2 conc. and BSC with BT at its

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central value. Similarly, Fig 3b describes the overlay plot for BSC and BT for a constant CaCl2 concentration. The constant terms applied for the plots were the central values defined

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as 4 min for BT and 1% for CaCl2. The shaded area within the overlay plot highlighted the

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most advantageous zone for a given set of variables. The most favorable ranges drawn from the overlay plot were found to be 1.0 -1.5 % w/v CaCl2, 22-27 ° brix for BSC, and 3.9-5.8

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min BT. The constraints criterion for numerical optimization was defined as maximum crispness; visual color in range and maximum OAA score for the FD crisp product. As such,

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the optimized conditions were derived as 1.38 % w/v CaCl2, 28.2 °brix BSC, and 5.2 min of BT. The numerically derived optimized conditions were in close proximity to the graphically

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derived ones. The derived responses from the optimized variables (Table 5) were comparable

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to their experimental counterparts indicating that the fitted models were appropriate. The

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optimization process was helpful in ensuring best possible OAA score of the crisps. 3.2 Drying kinetics

Fig. 4 represents the kinetics of the freeze-drying (FD), hot air-drying (HAD) and a

standard combination-drying (CD) protocols for moisture removal from the jackfruit bulbs. The moisture content of the jackfruit bulb was reduced at a faster rate in HAD. Both HAD and CD was found to take 14 hrs while FD took 20 hrs to remove the moisture from the samples up to a shelf-stable level of 4-7 %. In the case of FD, sublimation of moisture content through ice channels in the tissue did not change the natural structure (Pei et al., 2014) while during HAD rapid removal of moisture along with migration of solutes to the outer layer of the fruit led to hardening of the surface (case hardening) resulting in a compact tissue (Jayaraman et al., 1990). Combination-drying (CD) protocol having longest FD and

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shortest HAD periods was found to be a better combination due to occurrence of minimum shrinkage, higher rehydration ratios, desirable textural and color characteristics and acceptable OAA scores (Table 6). However, Phanindrakumar et al. (2001) reported removal of at least 30% moisture as more economical with respect to time and energy in case of

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combination drying involving FD followed by HAD in the case of carrots and pumpkin. Hence, a CD protocol consisting of 6 h FD and 8 h HAD removing 31.24 % and 40.58 %

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moisture respectively from jackfruit bulb slices and having a competitive OAA score was

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selected from among the various other combination-drying protocols having higher FD and lower HAD schedules. Pre-treatments, such as osmoblanching was also reported to impose a

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minor osmotic drying effect in the fruit tissue (Piga et al., 2004). Pore formation due to FD could be attributed to help in quick removal of moisture during further HAD (Krokida et al.,

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1998). 3.3 Shrinkage

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Drying of fruits induces several physico-chemical changes, including water activity

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(aw) and mobility of solutes such as sugars. These aspects in turn define the quality of the

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dried product in terms of features such as case hardening (Krokida et al., 2000). Monitoring of changes in structural and textural aspects could be advantageous in evaluating individual and combination-drying techniques. Use of FD could maintain the porous nature of the samples, giving lower shrinkage. The porosity was greatly affected by the extent of the HAD phase during CD. The degree of shrinkage was 50 % and 8 % in case of air and freeze-dried crisps respectively (Table 6). In FD, sublimation of water from the tissue could be accredited for the maintenance of pores and restriction in the occurrence of shrinkage (Krokida et al., 1998). Longer duration and higher drying temperatures involved in HAD resulted in faster loss of moisture but imparted a dense and shrunken texture to the product resulting in reduced porosity (Niamnuy et al., 2014). The longer duration of HAD in CD schedules, significantly (P < 0.05) increased the occurrence of shrinkage in the crisps.

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3.4 Rehydration ratio Dehydrated fruit and vegetable products could also be further processed or consumed after rehydration (Lewicki, 1998). Hot air-dried crisps of jackfruit bulbs showed lower rehydration ratio due to their compact tissue structure formed upon drying. In general, as the

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duration of HAD was increased, the samples recorded corresponding increase in shrinkage and hardness, which could be responsible for the lower rehydration ratio. However, a

cr

decrease in the FD phase in the CD schedule recorded a significant (P<0.05) decrease in

us

rehydration ratio up to about 43% as compared to the freeze-dried crisps (Table 6). Prevention of tissue collapse at the surface in the case of FD could result in a higher

an

rehydration ratio. The osmotic pretreatment has also been reported to lower the rehydration ratio in case of mango chips produced by explosion puffing (Zou et al., 2013).

M

3.5 Texture

The consumers often rate hardness and crispness as the most important textural

d

attributes of fruit crisps (Marzec et al., 2010). These two parameters were significantly

te

(P<0.05) affected by the drying schedule. Freeze-dried crisps had significantly (P<0.05)

Ac ce p

lower hardness and crispness values than those of hot air-dried samples (Table 6). Jagannath et al. (2001) reported FD to impart softness to the potatoes, and attributed it to lower hardness and chewiness. Decrease in the FD phase resulted in a significantly higher hardness value for combination-dried crisps. Solubilization of pectin, as well as shrinkage during HAD, could be attributed to the development of harder product whereas increased porosity due to sublimation and loss in elastic properties of cells may be responsible for a brittle texture in the case of freeze-dried crisps (Deng & Zhao, 2008). In case of CD having HAD followed by FD, formation of a harder external layer on the samples due to HAD hindered further moisture removal through FD and required a longer drying time, which ultimately yielded a finished product with an unacceptable texture (data not reported). 3.6 Color

43

Page 18 of 36

Instrumental color values have frequently been used for explaining the color changes in fresh as well as processed foods such as fruit crisps (Khalloufi & Ratti, 2003; Piga et al., 2004). Table 6 shows that lightness (L-) value and total color difference (∆E) between the samples was significantly (P<0.05) affected by different modes of drying. The results showed

ip t

that the higher L-values were recorded in case of freeze-dried crisps, indicating a lesser degree of browning (Ling et al., 2005). As the duration of HAD was increased, a decrease in

cr

L-value and a shift to reddish (hue) and a deeper (chroma) zone in the Hunter color

us

coordinates was recorded. Increased darkness in the color of crisps indicated the occurrence of maillard reaction. As compared to freeze-dried crisps, hot air-dried ones recorded

an

significant (P<0.05) changes in L-value (about 13%) as well as in total color. Exposure to high temperatures during HAD caused an increase in ∆E, which is related to changes in

M

contents of flavonoids or carotenoids (Ratti, 2001). Moreover, the overall changes in visual and textural attributes led to a significant (P<0.05) reduction in the OAA score of the crisps

te

3.7 Microstructure

d

obtained as a result of an increasing period of HAD (Table 6).

Ac ce p

A comparison of the microstructure of jackfruit bulb crisps clearly revealed the effect of different drying schedules. The SEM micrographs indicated that CD consisting of 6 h FD followed by 8 h HAD caused lesser damage to the microstructure of the samples compared to HAD (Fig. 5) and, at the end of the process, the tissue had greater porosity and a lower degree of shrinkage as compared to hot air-dried ones (Table 6). The micrograph of hot airdried crisps depicted a dense and shriveled structure with higher degree of tissue collapse. On the other hand freeze-dried crisps showed less tissue disintegration with intact capillaries (Acevedo et al., 2008). Similar results were reported for freeze-dried apple slices with a smaller extent of tissue disintegration and intact capillaries (Acevedo et al., 2008). Niamnuy et al., (2014) described the possibility of statistical analysis of microstructure by means of assigning numerical values to the microstructure image. Deng and Zhao (2008) pretreated

44

Page 19 of 36

apple cylinders with high-fructose corn syrup containing a Ca Salt as well as treatment with pulsed vacuum (PV), or ultrasound before freeze drying. The authors reported that the dried samples had a porous structure, minimal shrinkage, softer texture, better rehydration capacity, lighter color, and a slightly lower glass transition temperature as compared to hot-air dried

ip t

samples. 3.8 Shelf-stability

cr

The selected combination-dried crisps were subjected to evaluation for shelf stability.

us

Table 7 revealed that the changes at ambient temperature i.e. AT (22-32 °C) were minimal and significant only from the six month onwards. This corresponded to shelf life of 8 months

an

under ambient conditions and 4 months at a storage temperature of 37 °C. A slightly higher increase in aw was observed under AT storage due to the comparatively lower temperature

M

than storage at 37 °C. Absorption of moisture at an aw level of 0.35 and above has been reported to be responsible for the unacceptability of the crisp foods such as potato chips,

d

crackers, etc. (Katz and Labuza, 1981). Ascorbic acid and total carotenoid contents showed a

te

decreasing trend during storage. Retention of 45% and 37% of total carotenoids and ascorbic

Ac ce p

acid respectively, was recorded during AT storage and found to be a limiting factor in deciding the shelf life of the product. Storage under 37 °C conditions significantly (P<0.05) affected the color and texture of the product. Hardness of the dried products increased with increasing aw while crispness decreased (Konopacka et al., 2002). L- (lightness) and b(yellowness) values showed a decreasing trend while the a- value (redness) increased; this may be attributed to non-enzymatic browning and oxidation of carotenoids. Sensory evaluation of the jackfruit crisps revealed a better preference by the panelists for the samples stored under ambient temperature conditions. However, panelists observed better crispness in samples stored at 37 °C, which could be attributed to the lower uptake of moisture during storage. 4. Conclusions

45

Page 20 of 36

Optimization of pre-treatment consisting of Ca salt infusion and osmoblanching variables before drying jackfruit bulb slices was carried out using response surface methodology with crispiness, visual color (Hunter L×b value) and OAA scores as responses. The optimized conditions of pre-treatments for jackfruit bulb crisps were derived as 1.38 %

ip t

w/v CaCl2, 28.2 °brix BSC, and 5.2 min BT. Optimized pre-treatment conditions were applied for different mode of drying such as FD, HAD, as well as different CD schedules.

cr

The quality of the crisps obtained through various CD protocols as well as FD and HAD were

us

compared in terms of structural and textural aspects along with overall acceptability. A CD protocol consisting of FD for 6 h followed by HAD for 8 h was found to produce a

an

comparatively better quality crisps from jackfruit bulb slices in terms of rehydration ratio, shrinkage, instrumental texture, color values and sensory scores as compared to the hot air-

M

dried crisps. The selected combination-drying protocol gave a product comparable in quality to the freeze-dried crisps with minimal shrinkage and disorientation of cell wall integrity.

d

Shelf-stability in terms of physico-chemical and sensory attributes were evaluated for the

te

crisps from the optimized CD protocol. As such, the combination-dried crisps had a shelf life

Ac ce p

of 8 months under ambient (22-32 °C) and 4 months under 37 °C temperature conditions. The study showed that the optimized pretreatments could result in combination-dried jackfruit bulb crisps with best possible sensory attributes having potential for commercial processing. These dehydrated jackfruit bulb crisp could also be further processed as powder for incorporation in development of other food products. References

Acevedo, N.C., Briones, V., Buera, P., Aguilera, J.M., 2008. Microstructure affects the rate of chemical, physical and color changes during storage of dried apple discs. J. Food Eng., 85, 222-231.

46

Page 21 of 36

Ahrne, L., Prothon, F, Funebo, T., 2003. Comparison of drying kinetics and texture effects of two calcium pre-treatments before microwave-assisted drying of apple and potato. Int. J. Food Sci. Technol., 38, 411-420. AOAC, 1997. Official Methods of Analysis, 16th Edn. Ass. Off. Anal. Chem., Virginia,

ip t

U.S.A.

Contreras, C., Martin, M.E., Martinez-Navarrete, N., Chiralt, A., 2005. Effect of vacuum

cr

impregnation and microwave application on structural changes, which occurred

us

during air-drying of apple. LWT, 38, 471-477.

Deng, Y., Zhao, Y., 2008. Effect of pulsed vacuum and ultrasound osmo-pretreatments on

apples (Fuji). LWT, 41 (9), 1575-1585.

an

glass transition temperature, texture, microstructure and calcium penetration of dried

M

Fan, L., Zhang, M., Xiao, G., Sun, J., Tao, Q., 2005. The optimization of vacuum frying to dehydrate carrot chips. Int. J. Food Sci. Technol., 40, 911-919.

d

Fernandes, F.A.N., Gallao, M.I., Rodrigues, S., 2008. Effect of osmotic drying and

te

ultrasound pre-treatment on cell structure: melon drying. LWT, 41 (4), 604-610.

Ac ce p

Fernandes, F.A.N., Rodrigues, S., Gaspareto, O.C.P., Oliveira, E.L., 2006. Optimization of osmotic drying of papaya followed by air-drying. Food Res. Int., 39, 492-498.

Jagannath, J.H., Nanjappa, C., Dasgupta, D.K., Arya, S.S., 2001. Crystallization kinetics of precooked potato starch under different drying conditions (methods). Food Chem., 75, 281-286.

Jayaraman, K.S., Das Gupta, D.K., Babu Rao, N., 1990. Effect of pre-treatment with salt and sucrose on the quality and stability of dried cauliflower. Int. J. Food Sci. Technol., 25, 47-60. Jiang, H., Zhang, M., Mujumdar, A.S., Lim, R., 2014. Comparison of drying characteristic and uniformity of banana cubes dried by pulse-spouted microwave vacuum drying, freeze drying and microwave freeze drying’. J. Sci. Food Agric., 94 (9) 1827–1834.

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Page 22 of 36

John, P.J., Narasimham, P., 1998. Quality of blast-frozen and cryo-frozen ripe jackfruit bulbs. J. Food Sci. Technol., 35, 59-61. Katz, E.E., Labuza, T.P., 1981. Effect of water activity on the sensory crispness and mechanical deformation of snack food products. J. Food Sci. Technol., 46, 403-408.

ip t

Khalloufi, S., Ratti, C., 2003. Quality deterioration of freeze-dried foods as explained by their glass transition temperature and internal structure. J. Food Sci., 68 (3), 892-903.

cr

Konopacka, D., Plocharski, W., Beveridge, T., 2002. Water sorption and crispness of fat-free

us

apple chips. J. Food Sci., 67 (1), 87-92.

Krokida, M.K., Karathanos, V.T., Maroulis, Z.B., 1998. Effect of freeze drying conditions on

an

shrinkage and porosity of dried agricultural products. J. Food Eng., 35, 369-380. Krokida, M.K., Kiranoudis, C.T., Maroulis, Z.B., Marinos-Kouris, D., 2000. Drying related

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properties of apples. Drying Technol., 18 (6), 1251-1267.

Publi., Ottawa. 1637 pp.

d

Larmond, E., 1977. Laboratory methods for sensory evaluation of foods. Canada Dep. Agric.

te

Lewicki, P. P. (1998). Effect of pre-drying treatment, drying and rehydration on plant tissue

Ac ce p

properties: A review. International Journal of Food Properties, 1(1), 1-22. Ling, H., Birch, J., Lim, M., 2005. The glass transition approach to determination of drying protocols for color stability in dried pear slices. Int. J. Food Sci. Technol., 40, 921927.

Man, Y.B.C., Sin, K.K., 1997. Processing and consumer acceptance of fruit leather from the unfertilized floral parts of jackfruit. J. Sci. Food Agric., 75, 102-108.

Manimegalai, G., Krishnaveni, A., Saravana Kumar, R., 2001. Processing and preservation of jackfruit (Artocarpus heterophyllus L.) bar (thandra). J. Food Sci. Technol., 38, 529531. Marina, I.H., Velumuttu, O., Pekka, E.K., 1989. Carotenoids in finish foods: vegetables, fruits, and berries. J. Agric. Food Chem., 37, 655–659. 48

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Marzec, A., Kowalska, H., & Zadrożna, M. 2010. Analysis of instrumental and sensory texture attributes of microwave–convective dried apples. J. Texture Studies, 41(4), 417-439.

optimization using designed experiments. Wiley, New York.

ip t

Myers, R.H., Montgomery, D.C., 1995. Response surface methodology: Process and product

Niamnuy, C., Devahastin, S., Soponronnarit, S., 2014. Some recent advances in

cr

microstructural modification and monitoring of foods during drying: A review. J.

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Food Eng., 123, 148-156.

Nijhuis, H.H., Torringa, H.M., Muresan, S., Yuksel, D., Leguijt, C., Kloek, W., 1998.

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Approaches to improving the quality of dried fruit and vegetables. Trends Food Sci. Technol., 9, 13-20.

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Pani, P., Leva, A.A., Riva, M., Maestrelli, A., Torreggiani, D., 2008. Influence of an osmotic

Eng., 86 (1), 105-112.

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pre-treatment on structure-property relationships of air-dried tomato slices. J. Food

te

Pei, F., Yang, W., Shi, Y., Sun, Y., Mariga, A.M., Zhao, L., Fang, Y., Ma, N., An, X., Hu Q.,

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2014. Comparison of freeze-drying with three different combinations of drying methods and their influence on color, texture, microstructure and nutrient retention of button mushroom (Agaricus bisporus) slices. Food Biopro. Technol., 7(3), 702-710.

Phanindrakumar, H.S., Radhakrishna, K., Nagaraju, P.K., Vijaya Rao, D., 2001. Effect of combination drying on the physico-chemical characteristics of carrot and pumpkin. J. Food Proc. Preser., 25, 447-460.

Piga, A., Pinna, I., Ozer, K.B., Agabbio, M., Aksoy, U., 2004. Hot air dehydration of figs (Ficus carica L.): drying kinetics and quality loss. Int. J. Food Sci. Technol., 39, 793799.

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Rahman, M.A., Nahar, N., Jabbar, M.A., Mosihuzzaman, M., 1999. Variation of carbohydrate composition of two forms of fruit from jack tree (Artocarpus heterophyllus L.) with maturity and climatic conditions. Food Chem., 65, 91-97.

products. Tata McGraw Hill Publishing Company, New Delhi.

ip t

Ranganna, S., 1986. Handbook of analysis and quality control for fruit and vegetable

Ratti, C., 2001. Hot air and freeze-drying of high value foods: a review. J. Food Eng., 49,

cr

311-319.

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Saxena A., Bawa A.S., Raju P.S., 2009. Optimization of a multi-target preservation technique for jackfruit (Artocarpus heterophyllus L.) bulbs. J. Food Eng., 91 (1), 18-28.

an

Saxena, A., Bawa, A.S., Raju, P.S., 2008. Use of modified atmosphere packaging to extend

Food Eng., 87 (4), 455-466.

M

shelf-life of minimally processed jackfruit (Arotocarpus heterophyllus L.) bulbs. J.

Saxena, A., Bawa, A.S., Raju, P.S., 2012. Effect of minimal processing on quality of jackfruit

d

(Artocarpus heterophyllus L.) bulbs using response surface methodology. Food

te

Biopro. Technol., 5 (1), 348-358.

Ac ce p

Saxena, T.M., Saxena, A., Raju, P.S., 2013. Development of value added products from jackfruit for small and medium enterprises. Ind. Food Packer, 67 (2), 95-104.

Schadle, E.R., Burner, E.E., Talley, L.J., 1983. Forced air-drying of partially freeze-dried compressed carrot bars. J. Food Sci., 48, 193-196.

Seow, C.C., Shanmugam, G., 1992. Storage stability of canned jackfruit (Artocarpus heterophyllus) juice at tropical temperature. J. Food Sci. Technol., 29, 371-374.

Torreggiani, D., Toledo, R.T., Bertolo, G., 1995. Optimization of vapor induced puffing in apple drying. J. Food Sci., 60 (1), 181-185. Zheng, J., Zhang, F., Song, J., Lin M., Kan J., 2014. Effect of blanching and drying treatments on quality of bamboo shoot slices. Int. J. Food Sci. Technol., 49(2), 531540.

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Zou, K., Teng, J., Huang, L., Dai, X., Wei, B., 2013. Effect of osmotic pretreatment on

Ac ce p

te

d

M

an

us

cr

ip t

quality of mango chips by explosion puffing drying. LWT, 51 (1), 253-259.

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Page 26 of 36

Table 1 - Pretreatment variables and their levels for Box-Behnken design in coded and uncoded form used for jackfruit bulb crisps -1

0

1

CaCl2 (% w/v)

X1

0.5

1.0

1.5

Blanching solution concentration (°brix)

X2

10

20

30

Blanching time (min)

X3

2

4

6

cr

ip t

Symbols

Table 2 -Experimental design used and values of response for pretreatment

Run

Blanching

Blanching Crispness Visual color

(w/v %) solution

time

(N)

(°brix) 10

4

3.76

2484

6.56

2

1.5

10

4

4.77

2504

7.19

3

0.5

30

4

4.36

2275

7.53

4

1.5

30

4

5.09

2305

8.18

5

0.5

20

2

3.77

2385

6.90

6

1.5

20

2

4.71

2403

7.36

7

0.5

20

6

4.23

2327

7.21

8

1.5

20

6

5.07

2358

8.03

1.0

10

2

3.81

2482

6.84

1.0

30

2

4.29

2326

7.88

1.0

10

6

4.35

2482

7.54

1.0

30

6

4.77

2233

8.40

1.0

20

4

4.70

2373

7.94

1.0

20

4

4.82

2379

8.07

15

1.0

20

4

4.70

2373

7.94

16

1.0

20

4

4.82

2379

8.07

17

1.0

20

4

4.69

2373

7.94

10 11 12 13 14

te

Ac ce p

9

M

0.5

d

1

OAA Score

(Hunter L × b value)

an

Concentration ( min )

us

Experiment CaCl2

52

Page 27 of 36

Table 3 - Analysis of variance of the responses for the fitted second order polynomial model as a function of pretreatment variables for jackfruit bulb crisps Source

df

Sum of squares Crispness (N)

Visual color

OAA Score

ip t

(Hunter L × b value) Regression First order terms

3

2.386*

88669.91*

Second order terms

6

0.487*

3413.17*

Total

9

2.873

92083.08

Residual

7

0.024

60.68

0.03

Lack of Fit

3

0.005

13.60

0.01

Pure error

4

0.018

Corrected Total

16

2.897

an

us

cr

1.24* 4.53

47.08

0.02

92143.76

4.56

M

*Significant at 1% level

3.29*

Table 4 - Regression coefficients of the fitted second-order polynomials representing the

d

relationship between the responses and variables Crispness (N)

te

Coefficients

4.746*

Ac ce p

ßo

Visual color (Hunter L × b value)

OAA Score

2375.41*

7.992*

Linear

ßCaCl2 ß Blanch. sol. conc.

0.440*

12.44*

0.320*

0.228*

-101.63*

0.483*

ß Blanching time

0.230*

-24.52*

0.275*

ß CaCl2 * Blanch. sol. conc.

-0.070*

2.46

0.005

ß CaCl2 * Blanching time

-0.025

3.10

0.090*

ß Blanch. sol. conc. * Blanching time

-0.015

-23.24*

-0.045

-0.056

2.03

-0.459*

-0.196*

14.33*

-0.169*

-0.246*

-9.23*

-0.159*

0.992

0.999

0.994

Interaction

Quadratic ßCaCl2

2

ß Blanch. sol. conc. ß Blanching time

2

2

R2 *Significant at 5% level.

53

Page 28 of 36

ip t cr

different drying schedules (n=3, nx=6, ny=10).

us

Table 6- Shrinkage, rehydration ratio, texture, color and overall acceptability (OAA) scores of jackfruit bulb crisps with respect to

Shrinkage (%)

Rehydration ratio

Hardness (N) x

Crispness (N) x

L-value x

∆E x

OAA Score y

FD (20 h)

7.8e

3.28a

18.28f

4.51f

79.11a

0.0

8.34a

CD (10 h FD + 4

18.4d

2.81b

21.81e

4.84e

75.54b

11.1e

7.54a

24.3c

2.56bc

22.82d

4.97de

74.27c

14.7d

7.36ab

30.5bc

2.34c

23.98c

5.08d

73.79c

20.9cd

7.17b

37.1b

2.11d

24.53c

5.21c

71.82d

23.7c

6.98c

1.86de

25.32b

5.32b

70.45e

29.7b

6.79cd

1.61e

26.23a

5.43a

69.22f

33.4a

6.60d

h HAD) CD (8 h FD + 6 h

CD (6 h FD + 8 h

ed

HAD)

h HAD) CD (2 h FD + 12

43.2a

h HAD) 49.7a

Ac

HAD (14 h)

ce pt

HAD) CD (4 h FD + 10

M an

Drying conditions

FD = freeze-dried; HAD = hot air-dried; CD = combination-dried. Mean value in each column with different superscript differs significantly (P < 0.05).

29

Page 29 of 36

ip t cr

us

Table 7 - Changes in quality parameters of combination-dried (6 h FD+ 8 h AD) jackfruit bulb crisps during storage (n=3, nx=6, ny=10) Moisture

Period

Temp.

(%)

(m)

(°C)

8

Hardne

Crispness

OAA

(mg/100g)

(mg/100g)

L

b

ss x (N)

x

Score y

22.6a

73.1a 2.74a

24.09a

23.86a

5.08a

8.51a

20.0b

71.3b 2.79b

23.84b

24.70b

5.03b

7.68b

a

(N)

22-32

5.55bc

0.349b

3.22b

37

5.52b

0.347a

2.56cd

15.1d

70.2c 2.83c

23.51d

25.90d

5.05c

6.84d

22-32

5.74d

0.352d

2.72c

16.4c

69.3d 2.85cd

23.49c

25.70c

4.95ef

6.91c

37

5.62c

0.349b

1.58f

8.3f

65.7f

22.88f

27.90f

5.02d

5.25f

22-32

5.99f

0.355e

2.20e

12.7e

68.2e 2.92e

23.13e

26.90e

4.87f

6.02e

37

5.72d

0.350c

0.56g

1.2g

63.1g 2.97f

22.35h

29.70g

4.98e

3.58g

22-32 37

ed

3.56a

ce pt

6

Ascorbic Acid Hunter color values x

0.346a

Ac

4

Total Carotenoids

5.40a

0

2

aw x

M an

Storage Storage

2.90de

6.18g

0.359f

1.62f

8.4h

65.8f

2.98g

22.75g

27.94fg

4.79g

5.11f

5.81ef

0.352d

ND

ND

59.4h 3.05h

21.75i

31.73h

4.95ef

2.12h

Mean value in each column with different superscript differs significantly (P < 0.05).

30

Page 30 of 36

Table 5 - Optimized independent variables and predicted and experimental values of Optimum condition

CaCl2 (% w/v)

1.38

Blanching solution concentration (°brix)

28.26

Blanching time (min)

5.22

Response

Predicted value

Crispness (N)

4.80

Visual color (Hunter L × b value)

2301.21

OAA Score*

8.28

Actual value

cr

Variables

ip t

responses at optimum conditions (n=3, *n=10)

2302.85 ± 1.32

8.31 ± 0.04

Ac ce p

te

d

M

an

us

4.84 ± 0.03

54

Page 31 of 36

LIST OF FIGURE CAPTIONS Fig. 1. A typical force deformation curve for jackfruit bulb slice crisp sample Fig. 2. Contour plots for the effect of pretreatment variables on (a) crispness, (b) visual color

ip t

(Hunter L × b value) and (c) overall acceptability (OAA) scores for jackfruit bulb slice crisps Fig. 3. Superimposed contour plots of pretreatment variables for jackfruit bulb slice crisps as a function of (a) blanching solution concentration and CaCl2 concentrations for 4 min of

cr

blanching time (b) blanching solution concentration and blanching time at 1% CaCl2 combination-drying (6 h FD + 8h AD); (◊) hot air-drying

us

Fig. 4. Moisture content as a function of dehydration time. (□) freeze-drying; (Δ) Fig. 5. SEM-micrographs of (a) freeze-dried; (b) combination-dried (6 h FD+ 8h AD); & (c)

Ac ce p

te

d

M

an

hot air-dried sample of jackfruit bulbs slice crisps

33

Page 32 of 36

ip t cr us an M Ac ce p

te

d

Fig. 1

34

Page 33 of 36

Crispness (N)

Design-Expert® So ftware 1.50

Crispness 5.09

(A)

3.76

5

X1 = B: Blanch. sol. conc. X2 = A: CaCl2

4.8

1.00

ip t

CaCl2 (%)

Actual Factor C: Blanching time = 4.00

1.25

4.5 0.75

0.50 15.00

20.0 0

25.00

30.00

us

10.00

cr

4.2 4

Blanching solut ion concentrat ion (°brix)

6.00

Visual color 2503.56

Visual color (Hunter L × b value) (B)

an

Design-Expert® Software

2232.66

M

4.00

2404

2448

2361

2281

2321

d

Actual Factor A: CaCl2 = 1.00

5.00

Blanching time (min)

X1 = B: Blanch. sol. conc. X2 = C: Blanching time

te

3.00

2.00

Ac ce p

10.00

15.00

25.00

30.00

Blanching solution concentrat ion (°brix)

OAA Score

Design-Expert® So ftware OAA Score 8.4

20.00

6.00

(C)

Actual Factor B: Blanch. sol. conc. = 20.00

Blanching time (min)

6.56

X1 = A: CaCl2 X2 = C: Blanching time

5.00

8.15

8.04

4.00

7.51 7.83 3.00

7.11

7.51

2.00 0.50

0 .75

1.00

1.25

1.50

CaCl2 (%)

Fig. 2

Page 34 of 36

Overlay Plot

Design-Expert® Software 1.50

Overlay Plot Crispness Visual color OAA Score

(A)

OAA Score: 8.15 1.25

X1 = B: Blanch. sol. conc. X2 = A: CaCl2

CaCl2 (%)

ip t

Crispness : 4.8

1.00

Visual color: 2321

cr

Actual Factor C: Blanching time = 4.00

us

0.75

0.50 10.00

15.00

20.00

25.00

30.00

an

Blanching solution concentration (°brix)

Overlay Plot

Design-Expert® Software

Crispness Visual color OAA Score

(B)

Visua l color: 2321

d

Crispness : 4.8

4.00

te

Actual Factor A: CaCl2 = 1.00

5.00

Blanching time (min)

X1 = B: Blanch. sol. conc. X2 = C: Blanching time

M

6.00

Overlay Plot

OAA Score: 8.15

Ac ce p

3.00

2.00 10.00

15.00

20.00

25.00

30.00

Blanching solution concentration (°brix)

Fig. 3

36

Page 35 of 36

3.5

2.5

ip t

2.0 1.5 1.0

cr

M o istu re (g/g dry so lid s)

3.0

0.0 0

4

8

12 Drying Time (h)

16

20

24

Ac ce p

te

d

M

an

Fig. 4

us

0.5

a

b

c

Fig. 5

37

Page 36 of 36