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VIABILITY OF PRE-TREATMENT DRYING METHODS ON MANGO PEEL BY-PRODUCTS TO PRESERVE FLAVOURING ACTIVE COMPOUNDS FOR ITS REVALORISATION
Journal Pre-proof VIABILITY OF PRE-TREATMENT DRYING METHODS ON MANGO PEEL BYPRODUCTS TO PRESERVE FLAVOURING ACTIVE COMPOUNDS FOR ITS REVALORISATION
Rodrigo Oliver-Simancas, Ma Consuelo Díaz-Maroto, Ma Soledad Pérez-Coello, Ma Elena Alañón PII:
S0260-8774(20)30051-0
DOI:
https://doi.org/10.1016/j.jfoodeng.2020.109953
Reference:
JFOE 109953
To appear in:
Journal of Food Engineering
Received Date:
04 November 2019
Accepted Date:
31 January 2020
Please cite this article as: Rodrigo Oliver-Simancas, Ma Consuelo Díaz-Maroto, Ma Soledad PérezCoello, Ma Elena Alañón, VIABILITY OF PRE-TREATMENT DRYING METHODS ON MANGO PEEL BY-PRODUCTS TO PRESERVE FLAVOURING ACTIVE COMPOUNDS FOR ITS REVALORISATION, Journal of Food Engineering (2020), https://doi.org/10.1016/j.jfoodeng. 2020.109953
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Journal Pre-proof VIABILITY OF PRE-TREATMENT DRYING METHODS ON MANGO PEEL BY-PRODUCTS TO PRESERVE FLAVOURING ACTIVE COMPOUNDS FOR ITS REVALORISATION
Rodrigo Oliver-Simancas1, Mª Consuelo Díaz-Maroto1,2, Mª Soledad Pérez-Coello1, Mª Elena Alañón3*
1Area
of Food Science and Technology, Department of Analytical Chemistry and Food
Sience and Technology, Faculty of Chemical Sciences and Technologies, University of Castilla-La Mancha, Avda. Camilo José Cela 10, 13071, Ciudad Real, Spain. 2Regional
Institute for Applied Scientific Research (IRICA), Area of Food Science and
Technology, University of Castilla-La Mancha. Avda. Camilo José Cela, 10, 13071 Ciudad Real, Spain.
3Area
of Food Science and Technology, Department of Analytical Chemistry and Food
Sience and Technology, Higher Technical School of Agronomic Engineering, University of Castilla-La Mancha. Ronda de Calatrava 7, 13071, Ciudad Real, Spain.
* Corresponding
author:
Tel.: [34] 926295300 Ext. 3285 E-mail: [email protected]
1
Journal Pre-proof Abstract Mango peel is regarded as a natural source of valuable aromatic compounds. However, in order to promote its valorization, stabilisation processes must be carried out due to the significant water activity of this by-product. A comprehensive study on the mango peel volatile composition effects of different dehydration methods was carried out: two oven drying treatments at 45º C during 18 h and at 60 ºC for 12 h as well as a freeze-drying treatment. Results showed that both lyophilisation and oven drying at 60 ºC lead to substantial losses of representative aromatic compounds such as monoterpenes and sesquiterpenes as well as the generation of undesirable ones such as furans when high temperature was applied. Oven drying mango peels at 45 ºC for 18 h was revealed as the best choice to preserve the chemical composition of fresh samples. The application of these conditions diminished the losses of valuable volatile compounds such as monoterpenes, sesquiterpenes meanwhile could increase the quantities of appreciated compounds such as C13-norisoprenoids. This study provides useful information to carry out the recovery and exploitation of mango peel by-products as natural source of valuable flavouring compounds by food and cosmetic industries.
Keywords Mango peels; revalorization; drying methods; volatile composition; flavouring active compounds; morphological changes
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Journal Pre-proof 1. Introduction Fruit and vegetable processing industry is the one which generates the most biowastes (Baiano, Baiano, & Antonietta, 2014). Added to this disturbing fact and since this group of food is recognized for presenting high quantities of valuable compounds (Banerjee et al., 2017), there exists a necessity to revalorize those by-products in order to contribute to the environmental sustainability and make industry activities more profitable. Mango (Mangifera indica L.) is a distinguished tropical fruit due to its appealing sensorial features and health-promoting activities. Mango is not only consumed as fresh fruit but also is commercialised in several formats because of its seasonal character. Therefore, there exist an extensive generation of wastes due to all these processes. Mango’s kernels and peels are the principal bio-wastes produced reaching percentages up to 35-55% (Ayala-Zavala et al., 2011). Incorrect management of these biomass leads to serious environmental pollution problems and also could result in economic losses for the industry. Several studies have reported the potentially added value mango wastes present, especially as a source of functional and nutraceutical ingredients derived from all the bioactive compounds existing in those fractions discarded (Ajila, Bhat, & Prasada Rao, 2007; Asif et al., 2016; Jahurul et al., 2015; Koubala, Kansci, Garnier, Thibault, & Ralet, 2013; Maisuthisakul & Gordon, 2009). There are not few the researches already executed in order to exploit the bioactive health-related compounds derived from mango wastes, but scarcely any about odour-active applications. Food and cosmetic flavourings often derive from synthetical origins. Despite not considering them harmful for human consumption in permitted doses, their presence in food and cosmetic labelling may cause discomfort to consumers (Zhong, Wu, Chen, Huang, & Hu, 2018). Recently the
3
Journal Pre-proof feasibility of using mango by-products as a natural source of valuable odour active compounds has been explored (Oliver-Simancas et al., 2019). Results pointed out mango peel as excellent flavouring matrix whose appreciated odour-active compounds were found even in larger quantities than in the edible mango fraction. This fact encouraged the revalorization of mango peels as a source of natural flavourings due to the appreciated sensorial features of mango, which may be considered an alternative for exploiting those by-products. However, the main inconvenience of mango peel revalorization seems to be the limited lifetime those products have. Usually, mango peels present humidity contents up to 90 %, which make them highly susceptible to enzymatic and microbiological degradations. Therefore, it is required a stabilization process in order to preserve them until their revalorization use. Nevertheless, those treatments may cause several changes in the chemometric profile. Indeed, several studies have been faced this issue with the aim to evaluate the better drying method to assure the functional properties of mango peel (Dorta, Lobo and González, 2012; Singh Sogi et al., 2013). However, the effect of drying methods on the odour-active compounds from mango peel has not been addressed until now. Therefore, the aim of this work was to accomplish a technological study in order to evaluatethe effect of three different drying methods (oven drying at different temperatures and freeze-drying) on the volatile composition which was analyzed by HSSPME coupled to GC-MS. This will provide crucial information to industries regarding the proper method to stabilize and preserve the quality of mango peel from a flavouring point of view.
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Journal Pre-proof 2. Material and methods 2.1. Mango peel and sample preparation. Around fifty mangoes from Osteen variety cultivated in Tropical Coast were provided at its ideal ripening stage (15.10± 0.03 ºBrix) by Miguel García Sánchez e Hijos S.A. (Motril, Spain) in November 2018. A superficial washing using warm tap water was executed in order to get rid of the possible dirt existing on the mango’s skins. A hand peeler was used to obtain mango peels, which were kept under refrigeration conditions in order to avoid losses or changes on their volatile profiles. The pool of peels was then homogenized and divided into four batches. “Fresh” batch did not receive any drying treatment beyond refrigeration conditions until sample analysis. In this batch the volatile composition was the native one, so fresh batch act as control and the moisture content of sample was 72.3 %. Two batches were oven dried under different combination of times and temperatures (conditions previously optimized) with the objective of reducing the moisture content under 8%: “dried at 45 ºC” for 18 h (D45) whose moisture content was 7.97 %, and “dried at 60 ºC” for 12 h (D60) with a moisture percentage of 6.85 %. The last batch, “Freeze-dried” (FD) sample, was frozen at −80 °C and then freeze-dried under vacuum (1.1 × 10−2 mbar) with a temperature of −53.2 ºC using a “Cryodos– 50 lyophilizer” (Telstar, Barcelona, Spain). The final moisture content of frezed-dried sample was 6.91 %. After drying treatment, the moisture content fresh and drying samples was determined by the international standard method adapted (ISO 1442:1997). Samples from each batch were milled for their homogenization and keep under refrigeration conditions until their analysis.
2.2. Analysis of volatile profile from mango peel by HS–SPME/GC–MS
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Journal Pre-proof Volatile compounds were determined by head space solid phase microextraction (HS-SPME) and gas chromatography coupled to mass spectrometry (GC–MS). A triple SPME fibre of DVB/CAR/PDMS 50/30 μm (Supelco Co., Bellefonte, PA, USA), previously conditioned at 270 °C during 30 min, was used. In a 10 mL capped vial, 2 g for fresh sample and 0.5 g for dried ones were mixed with 5 mL of Milli-Q water, 0.6 g of NaCl and 30 μL of 4-nonanol (0.15 g/L) used as an internal standard. The mixture was homogenized for 30 s (Ika Works Ultra-TurraxT 10). Following, the HS-SPME analysis was carried out by a CombiPal G6500-CTC (Agilent Technologies). The fibre was preheated at 40 °C during 1 min in the extraction device and exposed to the headspace of the vial at 60 °C for 30 min under continuous stirring, 250 rpm. Immediately it was transferred to the GC injector and volatile compounds desorbed at 260 °C for 5 min (Oliver-Simancas et al., 2019). GC–MS analysis was executed in splitless mode during 0.30 min with a purge flow to split vent of 50 mL/min on a 6890 N Agilent gas chromatograph coupled to a 5973 N Agilent Mass Detector. Volatile compounds were separated on a polar DBWAX UI column (60 m × 0.25 mm i.d.; 0.25 μm film thickness) from Agilent Technologies, Inc. The carrier gas was helium at 1 mL/min and the oven temperature follow was that previously proposed by Oliver-Simancas et al., 2019. Column temperature was programmed at 40 °C which was ramped at 2 °C/min to 160 °C, and then increasing 10 °C/min to 220 °C. The MS worked in the electron impact mode with an electron energy of 70 eV, the ion source temperature was 230 °C and the scanning was made from 45 to 550 a.m.u. Identification process was carried out by means of standards and for those not available, a tentative identification was performed by comparison of their linear retention index (LRI) and mass spectra with spectral data found on Wiley G 1035 A, NBS75K and NIST14 libraries or reported in bibliography.
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Journal Pre-proof All analysis were done in triplicate and results were expressed in micrograms per gram of dry extract matter (µg/gDM) except for furanic and C13-norisoprenoids compounds, which were expressed in nanograms per gram of dry matter (ng/gDM).
2.3. Statistical analysis Statistical analysis was executed by using the IBM SPSS statistics v.24.0 for Windows statistical package. The volatile data set was submitted to the StudentNewman-Keuls’stest in order to find significant differences between samples. A principal component analysis (PCA) was carried out in order to simplify the complexity of the data set and spotlight the main contributors to the variance amongst the different samples studied. 2.4. Scanning Electron Microscopy Analyses by HRSEM Microstructures of fresh and dried samples were examined by using a scanning electron microscope, ZEISS GeminiSEM 500coupled to Cryo-SEM PP3010 Quorum. The inner part of the fresh and dried mango peels was observed at different magnification levels. Samples were placed on one surface of a two-sided adhesive tape that was fixed to the sample support. Samples were coated with gold particles under vacuum condition and then were observed on a Quanta-200 scanning electron microscope (SEM, Quanta-200, FEI, Netherlands) for outer surface using an accelerating voltage of 5 kV. The accelerating voltage was 2.00 kV and the magnification range were from x 400 and x 945.
3. Results and discussion
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Journal Pre-proof Sixty-seven flavouring compounds were identified and grouped into 8 different families:
hydrocarbon
monoterpenes,
oxygenated
monoterpenes,
hydrocarbon
sesquiterpenes, alcohols, aldehydes, ketones, furans, and C13-norisoprenoids (Table 1 – 4). In fresh sample, which was used as control, hydrocarbon monoterpenes and sesquiterpenes were by far the dominant groups accounting for 70.5 % and 29.0 % respectively, referred to the total volatile profile for fresh peel samples. At lower levels, aldehydes contributed 0.23 %, alcohols 0.12 %, oxygenated monoterpenes 0.05 %, ketones 0.08 % and furans and C13-norisoprenoids < 0.01 %.
3.1. Effect of drying methods on volatile composition of mango peels. 3.1.1. Monoterpenes and sesquiterpenes Hydrocarbon monoterpenes group was dominated by 3-carene in every sample (Table 1). This is in agreement with other authors who reported this compound as the major one in other mango cultivars such as Kent, Haden, Keitt, or Tommy Atkins (Andrade, Maia, & Zoghbi, 2000; Bonneau et al., 2016; Pino & Mesa, 2006). Beyond 3carene, great quantities of α-terpinolene, α-phellandrene, and D-Limonene were found. These compounds are regarded as key odorants due to their sensorial features described as citrus and resinous responsible for the typical mango-like aroma described in the literature (MacLeod & de Troconis, 1982). Nevertheless,
changes
occurred
during
treatments
to
hidrocarbonated
monoterpenes. In general, terms, almost all hidrocarbonated compounds decreased their amounts after the application of drying methods. Regards to the aforementioned compounds, lower losses were detected in those mango peels underwent to oven-dried at 45 ºC compared to the other two methods. This behaviour was also confirmed for practically all monoterpenes. In general terms, oven-drying at 45 ºC was the most
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Journal Pre-proof respectful treatment as it caused a loss of 15.7 % compared to the fresh samples, not being a significant change according to the Student-Newman-Keuls test (α = 0.05). Oven drying at 60 ºC and freeze-drying caused significant higher losses of 59.7 % and 77.7 % respectively. This fact suggested that both high temperatures and vacuum conditions drove to hydrocarbon monoterpenes losses. Only two compounds, eucarvone and citral, were identified as oxygenated monoterpenes providing a total of 0.07 µg/gDM in fresh mango peel. Eucarvone seemed to be more stable versus heat treatments and freeze-drying conditions. Contrary, citral, the most abundant compound in this group, was almost not detected in freeze-dried mango peel samples. However, citral concentrations increased in the oven dried samples, especially in those submitted to 45 ºC (0.06 to 0.13 µg/gDM). This fact suggested the citral enhancement by continuous exposure to warm air as it was previously reported in the literature (Degenhardt et al., 2014). However, no references explaining the formation mechanism were found. On the other hand, hidrocarbonated sesquiterpenes group was led by trans-βcarylophyllene, β-selienene,D-cadinene, α-gurjunene and α-humulene compounds among others contributing with 44.20 µg/gDM in fresh samples. Every hidrocarbonated compound was affected in detriment by the treatments applied since losses of 59.3 78.9 % were originated. This fact was in good agreement with those data reported in mango pulp by other authors (Bonneau et al, 2016). Likely to the previous group, significant differences were found on sesquiterpene content between the drying treatments applied. The oven dried of mango peels at 45 ºC during 18 hours preserved better the overall composition of sesquiterpenes which seemed to be more prone to decrease under higher temperatures or vacuum conditions. 3.1.2. Alcohols, aldehydes and ketones
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Journal Pre-proof Within alcohols group, it was difficult to find an overall tendency on how treatments affected the compounds belonging to this group. This fact may be explained because of the physico-chemical properties of alcohols. The already present alcohols in fresh samples are prone to evaporate under heat or freeze-drying treatments. Nevertheless, new ones could be generated as a result of hydrolysis reactions of glycosides compounds favoured by the temperatures applied during drying processes. This behaviour is already shown in the literature on mangoes samples (Bonneau et al., 2016) and other fruits (Franco et al., 2004). Even though total alcohols slightly increased due to the treatments, some clarifications should be pointed out. On the one hand, compounds such as (Z)-3-hexen-1-ol or 1-octanol decreased in the treated samples while on the other hand, similar compounds as 3-octanol and 2-ethyl-1-hexanol increased. As happened in the previous group, few differences can be found between the three treatments, especially between samples dried at 60 ºC and those submitted to freeze-drying. The thermal treatment using 45 ºC seemed to emphasize the appearance of alcohols. The reduction of these compounds when applying drying techniques could be counterbalanced through the release of alcohols present in their glycoside’s forms. Some of the aldehydes underwent an increase during the treatments. All the compounds detected from these groups were aliphatic aldehydes with the exception of benzaldehyde. It is particularly interesting to observe how the lyophilization process increased considerably the C6-aldehydes compounds such as hexanal (0.09 µg/gDM) and 2-hexenal (0.31 µg/gDM) compared to fresh samples (0.02 and 0.03 µg/gDM respectively). Aldehydes seem to be generated by oxidative and enzymatic reactions of fatty-acids amongst other causes (Belitz, Grosch, & Schieberle, 2009). Therefore, the increase of aldehydes observed in treated samples could be explained by this fact.
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Journal Pre-proof A general tendency explaining the behaviour of ketones regarding drying treatments applied was not found (Table 3). Concentrations of 1-octen-3-one were increased significantly as consequence of the thermal treatments as occurred with 4octanol. Meanwhile, the quantities of 4-nonanone observed in fresh samples (0.10 µg/g) were drastically decreased in all treated peels until concentrations of 0.02 and 0.03 µg/g. Despite the significative differences found, the most respectful treatment was thermal drying using 45 ºC. 3.1.3. Furanic compounds and C13-norisoprenoids Furanic compounds such as 2-pentylfural and furfural were also identified in mango peels. There were no differences between fresh samples and freeze-dried one's regards to the total content of the aforementioned furanic compounds. However, their total amounts increased in mango peels submitted to both thermal treatments, 45 and 60 ºC.This fact was more remarkable for furfural whose concentrations were significantly increased, especially when the highest temperature was applied. This phenomenon might be explained by the different carbohydrates pathways degradation such as nonenzymatic reactions or even by enzymatic reactions or by the simple heating of sugars in acidic conditions. C13-norisoprenoids compounds such as β-damascenone and β-ionone were also detected. Despite low concentrations found in mango peels, they present an extremely low threshold detection, 0.002 and 0.007 ppb for β-damascenone and β-ionone respectively (Kennedy & Cosnett, 2002). Due to this fact, both compounds have previously pointed out as key contributors to the overall aroma profile of several cultivars of mango by their fruity-floral-violet-like aroma (Pino, 2012; Pino and Mesa, 2006; Pino et al., 2005).
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Journal Pre-proof The concentrations of β-damascenone and β-ionone were enhanced by heat conditions and lead to the generation of these compounds. The same pattern has already reported in model studies and other fruit samples such as nectarines (Kashid et al., 2011; Sunthonvit, Srzednicki, & Craske, 2007). This fact seems to be attributable to the natural existence of these compounds in their glycosylated form whose hydrolysis catalized by enzymatic reactions and favoured by the temperature , could cause the release of their free forms (Skouroumounis & Sefton, 2000). This elucidation was in good agreement with other authors who also observed this C13-norisopreonids’ behaviour in other matrices (Sánchez-Palomo et al., 2009). Major quantities of these compounds (6.45 and 3.36 ng/g for β-damascenone and β-ionone respectively) were detected in those samples treated at 45 ºC suggesting that longer drying times favoured hydrolysis reactions.
3.2. Principal Component Analysis With the aim of highlighting the main changes in the volatile profile of mango peels due to the different drying methods applied, chemical data were submitted to a principal component analysis. The first two principal components explained nearly 81 % of the variance between the samples. Principal component 1 (PC1) explained almost 58 % of the variance. Figure 1 plots the samples on the coordinate grid defined by the first two principal components. PC1 separated fresh samples and those dried at 45 ºC from mango peels dried at 60 ºC and freeze-dried. A total of seventeen compounds contributed positively to the aforementioned separation (values ≥ 0.95) of the PC1 (Figure 2). They were primarily hidrocarbonated monoterpenes and sesquiterpenes such as isoterpinolene, γ-terpinene, trans-β-ocimene or α-humulene. These results showed the similarity between fresh samples and dried ones at 45 ºC.
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Journal Pre-proof On the other hand, the principal component 2 (PC2) explained 23% of the variance and caused the graphical separation of fresh and freeze-dried mango peels from both oven dried samples (Figure 1). In the case of PC2, not only hidrocarboanted sesquiterpenes (aromadendrene and γ-muurolene) contributed positively to the discrimination but also did the hidrocarbonated monoterpene α-cubebene, and two aldehydes such as nonanal and octanal (Figure 2). Major concentrations of these compounds were detected in those samples not submitted to thermal treatments. Contrary, 4-octanol, which also was pointed out as a significant contributor to the differentiation among drying treatments, exhibited larger amounts in the mango peels which were submitted to oven heating.
Therefore, based on the results, the best drying method to stabilize and preserve the volatile composition of mango peels for its flavouring revalorization was the oven heating using low temperature, 45 ºC, during 18 hours. This evidence contrasts with data reported in bibliography in which freeze-drying is outlined as the most proper drying method to assurance the polyphenol and chlorophyll contents as well as the antioxidant activity of mango peels for its re-utilization as nutraceuticals or functional ingredients (Dorta, Lobo & González, 2012). Consequently, depending on the revalorization purposes, mango peels should be treated with the most suitable drying method.
3.3. Scanning Electron Microscopy (SEM) Images SEM images were obtained from each sample used in this technological study in order to observe morphological changes caused by the different treatments applied (Figure 3). In both fresh and freeze-dried samples, it washighly recognizable cell
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Journal Pre-proof structure derived from the inner part of the peel which contained leftover pulp. In the case of the freeze-dried sample, cell structures seemed not to be damaged and inner parts of the cells appeared empty because of the sublimation (dehydration) process (Afonso et al., 2019). On the other hand, cell structures were not recognizable in oven dried mango peels.The leftover surface pulp disappeared in both samples as consequence of the thermal treatmentand spherical morphologies, related to pectins structure, were appreciated. The application of temperature for a considerable period of time seemed to result in demethoxylation of pectins which lead to the generation of such spherical structures as it was reported by other authors in guava fruit (Osorio, Carriazo, & Barbosa, 2011).
4. Conclusions The recovery and utilization of valuable compounds from mango peel byproduct as a natural flavouring agent have become an important aspect for its sustainable exploitation. Based on the results, the proposed process to reclaim the valuable flavors from mango peel is oven drying at 45 ºC during 18 hours. These conditions not only assure the stability of mango peel reducing the moisture content but also have been proven to be the best choice for the preservation of volatile compounds of fresh mango peel. From an industrial point of view, despite the longer drying times, the application of moderate temperature, 45 ºC, also entails
a reduction in the energy costs to carry out the
stabilization process at industrial level.
Acknowlegments:
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Journal Pre-proof Authors
thank
to
the
financial
support
of
the
Project
(SBPLY/17/180501/000509) from Junta de Comunidades de Castilla-La Mancha. Authors also thank to the Ibero-American Program of Science and Technology for Development, CYTED (118RT0543). R. Oliver-Simancas thanks to University of Castilla-La Mancha for the predoctoral grant. Authors are also grateful to the Company “Grupo Empresarial La Caña” for the mangoes traceability assurance and for its compromise with the research group and with the R+D+i.
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Journal Pre-proof https://doi.org/10.1016/J.FOODCHEM.2009.04.010 Oliver-Simancas, R., Muñoz, R., Díaz-Maroto, M.C., Pérez-Coello, M.S., Alañón, M.E. (2019). Mango by-products as source of valuable odor-active compounds. Submitted. Osorio, C., Carriazo, J. G., & Barbosa, H. (2011). Thermal and structural study of guava (Psidium guajava L) powders obtained by two dehydration methods. Química Nova, 34(4), 636–640. https://doi.org/10.1590/S0100-40422011000400016 Pino, J.A. (2012). Odour-active compounds in mango (Mangifera indica L. cv. Corazón). International Journal of Food Science and Technology, 47, 1944-1950. https://doi.org/10.1111/j.1365-2621.2012.03054.x Pino, J. A., & Mesa, J. (2006). Contribution of volatile compounds to mango (Mangifera indica L.) aroma. Flavour and Fragrance Journal, 21(2), 207–213. https://doi.org/10.1002/ffj.1703 Pino, J.A., Mesa, J., Muñoz, Y., Martí, M.P., Marbot, R. (2005). Volatile components from mango (Mangifera indica L.) cultivars. Journal of Agricultural and Food Chemistry, 53, 2213-2223. https://doi.org/10.1021/jf0402633 Sánchez-Palomo, E., Alañón, M. E., Díaz-Maroto, M. C., González-Viñas, M. A., & Pérez-Coello, M. S. (2009). Comparison of extraction methods for volatile compounds
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https://doi.org/10.1016/J.TALANTA.2009.05.019 Singh Sogi, D., Siddiq, M., Greiby, I., Dolan, K.D. (2013). Total phenolics, antioxidant activity, and functional properties of Tommy Atkins mango peel and kernel as affected
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19
Journal Pre-proof R. Oliver-Simancas: Investigation, validation, formal analysis, writing – original draft M.C. Díaz-Maroto: methodoloy, supervision M.S. Pérez-Coello: methodoloy, supervision M.E. Alañón: Conceptualization, writing – review and editing, visualization, project administration, funding acquisition, supervision.
Journal Pre-proof
Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
Journal Pre-proof
Figure 1. Graphical distribution of mango peel samples dried with different methods in comparison with fresh samples defined by PC1 and PC2 according to the PCA applied to volatile composition data.
Journal Pre-proof
Figure 2. Loadings of the main contributors to discrimination among different drying methods applied to mango peels and fresh ones based on the principal component analysis of volatile composition.
Journal Pre-proof
Figure 3. Scanning electron micrographs of fresh mango peel (FRESH), freeze-dried mango peel (FD), oven-dried mango peel at 45 ºC (D45) and oven-dried mango peel at 60 ºC (D60). The magnification was set as × 945 on FRESH and FD and x 400 on D45 and D60.
Journal Pre-proof Highlights
Mango peel is an natural source of odour-active compounds
Due to its high moisture, mango peel should be stabilised for its revalorisation
Drying methods should be optimized to avoid losses of volatile compounds
Oven drying at 45 ºC for 18 hours preserved better the chemical profile of mango peel
Journal Pre-proof Table 1. Hydrocarbonand oxygenated monoterpenes compounds detected in fresh and dried mango peel samples (µg/gDW, n = 3).
LRI
COMPOUNDS
FRESH MEAN
SD
DRIED AT 45 ºC MEAN
SD
DRIED AT 60 ºC MEAN
SD
FREEZE DRIED MEAN
SD
Hydrocarbon monoterpenes ---
α-Pinene
1030
α-Fenchene
1041
Camphene
1090
β-Pinene
1136
3-Carene
1153
α- Phellandrene
1166
o-Cymene
1169
α-Terpinene
1186
Sylvestrene
1188
D-Limonene
1200
β-phellandrene
1229
Cis-β-Ocimene
1235
α-Thujene
1240
ϒ-Terpinene
1246
Trans-β-Ocimene
1260
m-Cymene
1263
p-Cymene
1271
Isoterpinolene
1278
α-Terpinolene
1370
Trans-allo-ocymene
1427
o-Cymenene
1436
p-Cymenene
1457
α-Cubebene Hidrocarbonated monoterpenes
0.39 0.04 0.01 0.02 67.19 5.62 0.07 1.12 0.47 4.68 1.97 0.05 0.14 0.31 0.40 0.10 0.98 1.51 12.18 0.02 0.06 0.39 0.18 97.89
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.08b 0.00c 0.00c 0.00d 15.72b 0.47c 0.01b 0.23b 0.02d 0.98c 0.16c 0.00c 0.01c 0.03c 0.04d 0.01b 0.11c 0.09c 1.06d 0.00c 0.01 0.05b 0.03c 18.00b
0.37 0.04 0.01 0.01 61.33 3.95 0.08 0.87 0.35 3.31 1.48 0.03 0.10 0.21 0.20 0.10 0.98 0.96 8.51 0.02 0.07 0.35 0.06 83.38
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.08b 0.00c 0.00c 0.00c 5.86b 0.91b 0.00b 0.20b 0.07c 0.31b 0.31b 0.00b 0.01b 0.05b 0.02c 0.02b 0.06c 0.21b 1.10c 0.00b 0.01 0.02b 0.01b 8.13b
0.20 0.02 0.01 0.01 27.54 1.86 0.04 0.43 0.18 1.77 0.63 0.02 0.04 0.10 0.09 0.07 0.52 0.46 3.54 0.01 0.05 0.19 0.03 39.79
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.03a 0.00b 0.00b 0.00b 4.21a 0.12a 0.00a 0.02a 0.01b 0.28a 0.10a 0.00a 0.00a 0.02a 0.01b 0.00a 0.03b 0.09a 0.72b 0.00a 0.00 0.01a 0.00a 5.57a
0.13 0.01 0.00 0.01 16.37 0.89 0.04 0.24 0.11 1.02 0.38 0.01 0.03 0.06 0.04 0.06 0.37 0.22 1.69 0.01 0.06 0.16 0.17 22.07
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.02a 0.00a 0.00a 0.00a 3.20a 0.21a 0.00a 0.03a 0.01a 0.21a 0.08a 0.00a 0.01a 0.01a 0.01a 0.00a 0.03a 0.05a 0.43a 0.00a 0.00 0.03a 0.02c 4.28a
Oxygenated monoterpenes 1559
Eucarvone
1693
Citral Oxygenated monoterpenes
0.01 ± 0.00b 0.06 ± 0.00a 0.07 ± 0.00b
0.01 ± 0.00b 0.13 ± 0.00c 0.14 ± 0.00d
0.01 ± 0.00a 0.10 ± 0.01b 0.11 ± 0.01c
0.01 ± 0.00b ND 0.01 ± 0.00a
Values with different superscripts in the same row denoted significant differences according to the Student-Newman-Keuls test at p ˂ 0.05. Samples were defined according to the treatment applied: “Fresh”, no treatment applied; “Dried at 45 ºC”, oven dried at 45 for 18 h; “Dried at 60ºC”, oven dried at 60 ºC for 12h; “Freeze dried”, Freeze dried at -53.2 ºC and 1.1 x 10-2 mbar for 12 h.
Journal Pre-proof Table 2. Hydrocarbon sesquiterpenes compounds detected in fresh and dried mango peel samples (µg/gDW, n = 3)
LRI
COMPOUNDS
1492
α-Copaene
1532
α-Gurjunene
1541
β-Gurjunene
1576
Cis-β-Caryophyllene
1591
β-Elemene
1598
Trans-β-Caryophyllene
1608
Aromadendrene
1647
Alloaromadendrene
1649
Isocarilophyllene
1657
γ-Gurjunene
1670
α-Humulene
1677
γ-Selinene
1690
γ-Muurolene
1696
Viridiflorene
1712
Valencene (isomer I)
1716
Valencene (isomer II)
1721
β-Selinene
1725
α-Selinene
1758
D-Cadinene Hidrocarbonated sesquiterpenes
FRESH MEAN
3.85 5.24 0.16 0.25 0.05 11.94 0.14 0.59 0.26 0.23 4.10 0.16 0.28 0.88 0.33 0.23 7.65 1.09 6.77 44.20
SD
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.38c 0.24c 0.01d 0.03c 0.01b 3.12b 0.05c 0.05c 0.02d 0.01d 0.08d 0.05b 0.05b 0.09b 0.04b 0.04b 2.16c 0.16b 1.27b 6.56c
DRIED AT 45 ºC MEAN
1.78 1.89 0.06 0.16 0.02 4.93 0.03 0.26 0.13 0.08 2.77 0.13 0.10 0.24 0.20 0.12 4.35 0.50 0.26 18.00
SD
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.27b 0.36b 0.01c 0.01b 0.00a 0.38a 0.01a 0.02b 0.03c 0.02c 0.21c 0.01a,b 0.01a 0.02a 0.01a 0.01a 0.28b 0.02a 0.03a 1.19b
DRIED AT 60 ºC MEAN
1.42 1.34 0.04 0.08 0.01 3.14 0.02 0.16 0.08 0.05 1.71 0.09 0.06 0.18 0.14 0.08 2.62 0.29 0.28 11.79
SD
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.13b 0.06a 0.01b 0.00a 0.00a 0.50a 0.00a 0.03a 0.02b 0.00b 0.30b 0.03a,b 0.00a 0.02a 0.01a 0.01a 0.19a,b 0.04a 0.01a 0.90a,b
FREEZE DRIED MEAN
0.51 0.96 0.03 0.17 0.17 1.98 0.19 0.12 0.04 0.03 1.17 0.06 0.49 0.20 0.19 0.11 1.32 0.39 1.17 9.29
SD
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.11a 0.10a 0.00a 0.01b 0.01c 0.28a 0.02d 0.02a 0.01a 0.01a 0.19a 0.01a 0.08c 0.04a 0.08a 0.05a 0.16a 0.14a 0.19a 1.03a
Values with different superscripts in the same row denoted significant differences according to the Student-Newman-Keuls test at p ˂ 0.05. Samples were defined according to the treatment applied: “Fresh”, no treatment applied; “Dried at 45 ºC”, oven dried at 45 ºC for 18 h; “Dried at 60 ºC”, oven dried at 60 ºC for 12 h; “Freeze dried”, Freeze dried at -53.2 ºC and 1.1 x 10-2 mbar for 12 h.
Journal Pre-proof Table 3. Alcohols, aldehydes and ketones compounds detected in fresh and dried mango peel samples (µg/gDW, n = 3)
LRI
COMPOUNDS
FRESH MEAN
SD
DRIED AT 45 ºC MEAN
SD
DRIED AT 60 ºC MEAN
SD
FREEZE DRIED MEAN
SD
Alcohols 1387
4-Octanol
1390
(Z)-3-Hexen-1-ol
1399
3-Octanol
1496
2-Ethyl, 1-hexanol
1566
1-Octanol Alcohols
ND 0.10 ± 0.00c 0.01 ± 0.00a 0.01 ± 0.00a 0.04 ± 0.00b 0.16 ± 0.00a
0.01 0.04 0.16 0.03 0.02 0.27
± ± ± ± ± ±
0.00a 0.01b 0.02b 0.00b 0.00a 0.02c
0.01 0.01 0.16 0.02 0.02 0.22
± ± ± ± ± ±
0.00a 0.00a 0.02b 0.00b 0.00a 0.02b
ND 0.02 ± 0.00a 0.14 ± 0.00b 0.05 ± 0.01c 0.04 ± 0.00b 0.23 ± 0.01b
ND 0.02 ± 0.00a 0.02 ± 0.00a 0.03 ± 0.00a 0.04 ± 0.01a,b 0.11 ± 0.04b 0.02 ± 0.00a ND 0.06 ± 0.01a 0.01 ± 0.00a tr 0.32 ± 0.05a
0.04 0.05 0.02 0.26 0.03 0.04 0.07 0.04 0.10 0.01 0.01 0.67
± ± ± ± ± ± ± ± ± ± ± ±
0.01b 0.00c 0.00a 0.01c 0.01a 0.00a 0.00c 0.00b 0.01b 0.00 b 0.00b 0.03c
0.03 0.03 0.02 0.10 0.03 0.06 0.04 0.03 0.05 0.01 0.01 0.40
± ± ± ± ± ± ± ± ± ± ± ±
0.00a 0.01b 0.01a 0.01b 0.00a 0.00a 0.00b 0.00b 0.01a 0.00a 0.00a 0.03b
ND 0.09 ± 0.00d 0.08 ± 0.01b 0.31 ± 0.02d 0.05 ± 0.01b 0.15 ± 0.01c 0.03 ± 0.00a 0.01 ± 0.00a 0.05 ± 0.00a 0.01 ± 0.00a 0.01 ± 0.00a 0.80 ± 0.04d
0.01 ± 0.00a 0.10 ± 0.01b ND 0.11 ± 0.01d
0.05 0.03 0.01 0.09
± ± ± ±
0.00d 0.00a 0.00a 0.00c
0.03 0.02 0.01 0.06
± ± ± ±
0.00b 0.01a 0.00a 0.01b
0.01 0.03 0.02 0.05
Aldehydes ---
Pentanal
1065
Hexanal
1180
Heptanal
1215
2-Hexenal
1286
Octanal
1393
Nonanal
1430
2-Octenal-(E)
1465
2,4-Heptadienal
1499
Decanal
1522
Benzaldehyde
1537
2-Nonenal Aldehydes Ketones
1299
1-Octen-3-ona
1324
4-Nonanona
1337
5-Hepten-2-one, 6-methyl Ketones
± ± ± ±
0.00b 0.00a 0.00a 0.00a
Values with different superscripts in the same row denoted significant differences according to the Student-Newman-Keuls test at p ˂ 0.05. Samples were defined according to the treatment applied: “Fresh”, no treatment applied; “Dried at 45 ºC”, oven dried at 45 ºC for 18 h; “Dried at 60 ºC”, oven dried at 60 ºC for 12 h; “Freeze dried”, Freeze dried at -53.2 ºC and 1.1 x 10-2 mbar for 12 h.
Journal Pre-proof Table 4. Furanic and C13-norisoprenoids compounds detected in fresh and dried mango peel samples (ng/gDW, n = 3)
LRI
COMPOUNDS
FRESH MEAN
SD
DRYED AT 45 ºC MEAN
SD
DRYED AT 60 ºC MEAN
SD
FREEZE DRIED MEAN
SD
Furans 1226 1464
2-pentylfuran Furfural Furans
6.83 ± 0.69a,b 1.78 ± 0.09a 8.61 ± 0.69a
7.64 ± 0.19b 4.03 ± 0.39b 11.67 ± 0.56b
2.82 ± 0.10a ND 2.82 ± 0.10a
6.45 ± 0.52b 3.36 ± 0.26c 9.80 ± 0.48c
5.71 ± 0.48a 9.93 ± 1.09c 15.64 ± 0.62b
5.88 ± 0.76a 3.01 ± 0.24b 8.89 ± 0.67a
C13 norisoprenoids 1826
β-damascenone β-ionone C13 norisoprenoids
4.75 ± 1.77a,b 2.54 ± 0.28b 7.29 ± 1.58b
3.90 ± 0.34a 1.93 ± 0.41a 5.83 ± 0.63b
Values with different superscripts in the same row denoted significant differences according to the Student-Newman-Keuls test at p ˂ 0.05. Samples were defined according to the treatment applied: “Fresh”, no treatment applied; “Dried at 45 ºC”, oven dried at 45 ºC for 18 h; “Dried at 60 ºC”, oven dried at 60 ºC for 12 h; “Freeze dried”, Freeze dried at -53.2 ºC and 1.1 x 10-2 mbar for 12 h.
Rodrigo Oliver-Simancas, Ma Consuelo Díaz-Maroto, Ma Soledad Pérez-Coello, Ma Elena Alañón PII:
S0260-8774(20)30051-0
DOI:
https://doi.org/10.1016/j.jfoodeng.2020.109953
Reference:
JFOE 109953
To appear in:
Journal of Food Engineering
Received Date:
04 November 2019
Accepted Date:
31 January 2020
Please cite this article as: Rodrigo Oliver-Simancas, Ma Consuelo Díaz-Maroto, Ma Soledad PérezCoello, Ma Elena Alañón, VIABILITY OF PRE-TREATMENT DRYING METHODS ON MANGO PEEL BY-PRODUCTS TO PRESERVE FLAVOURING ACTIVE COMPOUNDS FOR ITS REVALORISATION, Journal of Food Engineering (2020), https://doi.org/10.1016/j.jfoodeng. 2020.109953
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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. © 2019 Published by Elsevier.
Journal Pre-proof VIABILITY OF PRE-TREATMENT DRYING METHODS ON MANGO PEEL BY-PRODUCTS TO PRESERVE FLAVOURING ACTIVE COMPOUNDS FOR ITS REVALORISATION
Rodrigo Oliver-Simancas1, Mª Consuelo Díaz-Maroto1,2, Mª Soledad Pérez-Coello1, Mª Elena Alañón3*
1Area
of Food Science and Technology, Department of Analytical Chemistry and Food
Sience and Technology, Faculty of Chemical Sciences and Technologies, University of Castilla-La Mancha, Avda. Camilo José Cela 10, 13071, Ciudad Real, Spain. 2Regional
Institute for Applied Scientific Research (IRICA), Area of Food Science and
Technology, University of Castilla-La Mancha. Avda. Camilo José Cela, 10, 13071 Ciudad Real, Spain.
3Area
of Food Science and Technology, Department of Analytical Chemistry and Food
Sience and Technology, Higher Technical School of Agronomic Engineering, University of Castilla-La Mancha. Ronda de Calatrava 7, 13071, Ciudad Real, Spain.
* Corresponding
author:
Tel.: [34] 926295300 Ext. 3285 E-mail: [email protected]
1
Journal Pre-proof Abstract Mango peel is regarded as a natural source of valuable aromatic compounds. However, in order to promote its valorization, stabilisation processes must be carried out due to the significant water activity of this by-product. A comprehensive study on the mango peel volatile composition effects of different dehydration methods was carried out: two oven drying treatments at 45º C during 18 h and at 60 ºC for 12 h as well as a freeze-drying treatment. Results showed that both lyophilisation and oven drying at 60 ºC lead to substantial losses of representative aromatic compounds such as monoterpenes and sesquiterpenes as well as the generation of undesirable ones such as furans when high temperature was applied. Oven drying mango peels at 45 ºC for 18 h was revealed as the best choice to preserve the chemical composition of fresh samples. The application of these conditions diminished the losses of valuable volatile compounds such as monoterpenes, sesquiterpenes meanwhile could increase the quantities of appreciated compounds such as C13-norisoprenoids. This study provides useful information to carry out the recovery and exploitation of mango peel by-products as natural source of valuable flavouring compounds by food and cosmetic industries.
Keywords Mango peels; revalorization; drying methods; volatile composition; flavouring active compounds; morphological changes
2
Journal Pre-proof 1. Introduction Fruit and vegetable processing industry is the one which generates the most biowastes (Baiano, Baiano, & Antonietta, 2014). Added to this disturbing fact and since this group of food is recognized for presenting high quantities of valuable compounds (Banerjee et al., 2017), there exists a necessity to revalorize those by-products in order to contribute to the environmental sustainability and make industry activities more profitable. Mango (Mangifera indica L.) is a distinguished tropical fruit due to its appealing sensorial features and health-promoting activities. Mango is not only consumed as fresh fruit but also is commercialised in several formats because of its seasonal character. Therefore, there exist an extensive generation of wastes due to all these processes. Mango’s kernels and peels are the principal bio-wastes produced reaching percentages up to 35-55% (Ayala-Zavala et al., 2011). Incorrect management of these biomass leads to serious environmental pollution problems and also could result in economic losses for the industry. Several studies have reported the potentially added value mango wastes present, especially as a source of functional and nutraceutical ingredients derived from all the bioactive compounds existing in those fractions discarded (Ajila, Bhat, & Prasada Rao, 2007; Asif et al., 2016; Jahurul et al., 2015; Koubala, Kansci, Garnier, Thibault, & Ralet, 2013; Maisuthisakul & Gordon, 2009). There are not few the researches already executed in order to exploit the bioactive health-related compounds derived from mango wastes, but scarcely any about odour-active applications. Food and cosmetic flavourings often derive from synthetical origins. Despite not considering them harmful for human consumption in permitted doses, their presence in food and cosmetic labelling may cause discomfort to consumers (Zhong, Wu, Chen, Huang, & Hu, 2018). Recently the
3
Journal Pre-proof feasibility of using mango by-products as a natural source of valuable odour active compounds has been explored (Oliver-Simancas et al., 2019). Results pointed out mango peel as excellent flavouring matrix whose appreciated odour-active compounds were found even in larger quantities than in the edible mango fraction. This fact encouraged the revalorization of mango peels as a source of natural flavourings due to the appreciated sensorial features of mango, which may be considered an alternative for exploiting those by-products. However, the main inconvenience of mango peel revalorization seems to be the limited lifetime those products have. Usually, mango peels present humidity contents up to 90 %, which make them highly susceptible to enzymatic and microbiological degradations. Therefore, it is required a stabilization process in order to preserve them until their revalorization use. Nevertheless, those treatments may cause several changes in the chemometric profile. Indeed, several studies have been faced this issue with the aim to evaluate the better drying method to assure the functional properties of mango peel (Dorta, Lobo and González, 2012; Singh Sogi et al., 2013). However, the effect of drying methods on the odour-active compounds from mango peel has not been addressed until now. Therefore, the aim of this work was to accomplish a technological study in order to evaluatethe effect of three different drying methods (oven drying at different temperatures and freeze-drying) on the volatile composition which was analyzed by HSSPME coupled to GC-MS. This will provide crucial information to industries regarding the proper method to stabilize and preserve the quality of mango peel from a flavouring point of view.
4
Journal Pre-proof 2. Material and methods 2.1. Mango peel and sample preparation. Around fifty mangoes from Osteen variety cultivated in Tropical Coast were provided at its ideal ripening stage (15.10± 0.03 ºBrix) by Miguel García Sánchez e Hijos S.A. (Motril, Spain) in November 2018. A superficial washing using warm tap water was executed in order to get rid of the possible dirt existing on the mango’s skins. A hand peeler was used to obtain mango peels, which were kept under refrigeration conditions in order to avoid losses or changes on their volatile profiles. The pool of peels was then homogenized and divided into four batches. “Fresh” batch did not receive any drying treatment beyond refrigeration conditions until sample analysis. In this batch the volatile composition was the native one, so fresh batch act as control and the moisture content of sample was 72.3 %. Two batches were oven dried under different combination of times and temperatures (conditions previously optimized) with the objective of reducing the moisture content under 8%: “dried at 45 ºC” for 18 h (D45) whose moisture content was 7.97 %, and “dried at 60 ºC” for 12 h (D60) with a moisture percentage of 6.85 %. The last batch, “Freeze-dried” (FD) sample, was frozen at −80 °C and then freeze-dried under vacuum (1.1 × 10−2 mbar) with a temperature of −53.2 ºC using a “Cryodos– 50 lyophilizer” (Telstar, Barcelona, Spain). The final moisture content of frezed-dried sample was 6.91 %. After drying treatment, the moisture content fresh and drying samples was determined by the international standard method adapted (ISO 1442:1997). Samples from each batch were milled for their homogenization and keep under refrigeration conditions until their analysis.
2.2. Analysis of volatile profile from mango peel by HS–SPME/GC–MS
5
Journal Pre-proof Volatile compounds were determined by head space solid phase microextraction (HS-SPME) and gas chromatography coupled to mass spectrometry (GC–MS). A triple SPME fibre of DVB/CAR/PDMS 50/30 μm (Supelco Co., Bellefonte, PA, USA), previously conditioned at 270 °C during 30 min, was used. In a 10 mL capped vial, 2 g for fresh sample and 0.5 g for dried ones were mixed with 5 mL of Milli-Q water, 0.6 g of NaCl and 30 μL of 4-nonanol (0.15 g/L) used as an internal standard. The mixture was homogenized for 30 s (Ika Works Ultra-TurraxT 10). Following, the HS-SPME analysis was carried out by a CombiPal G6500-CTC (Agilent Technologies). The fibre was preheated at 40 °C during 1 min in the extraction device and exposed to the headspace of the vial at 60 °C for 30 min under continuous stirring, 250 rpm. Immediately it was transferred to the GC injector and volatile compounds desorbed at 260 °C for 5 min (Oliver-Simancas et al., 2019). GC–MS analysis was executed in splitless mode during 0.30 min with a purge flow to split vent of 50 mL/min on a 6890 N Agilent gas chromatograph coupled to a 5973 N Agilent Mass Detector. Volatile compounds were separated on a polar DBWAX UI column (60 m × 0.25 mm i.d.; 0.25 μm film thickness) from Agilent Technologies, Inc. The carrier gas was helium at 1 mL/min and the oven temperature follow was that previously proposed by Oliver-Simancas et al., 2019. Column temperature was programmed at 40 °C which was ramped at 2 °C/min to 160 °C, and then increasing 10 °C/min to 220 °C. The MS worked in the electron impact mode with an electron energy of 70 eV, the ion source temperature was 230 °C and the scanning was made from 45 to 550 a.m.u. Identification process was carried out by means of standards and for those not available, a tentative identification was performed by comparison of their linear retention index (LRI) and mass spectra with spectral data found on Wiley G 1035 A, NBS75K and NIST14 libraries or reported in bibliography.
6
Journal Pre-proof All analysis were done in triplicate and results were expressed in micrograms per gram of dry extract matter (µg/gDM) except for furanic and C13-norisoprenoids compounds, which were expressed in nanograms per gram of dry matter (ng/gDM).
2.3. Statistical analysis Statistical analysis was executed by using the IBM SPSS statistics v.24.0 for Windows statistical package. The volatile data set was submitted to the StudentNewman-Keuls’stest in order to find significant differences between samples. A principal component analysis (PCA) was carried out in order to simplify the complexity of the data set and spotlight the main contributors to the variance amongst the different samples studied. 2.4. Scanning Electron Microscopy Analyses by HRSEM Microstructures of fresh and dried samples were examined by using a scanning electron microscope, ZEISS GeminiSEM 500coupled to Cryo-SEM PP3010 Quorum. The inner part of the fresh and dried mango peels was observed at different magnification levels. Samples were placed on one surface of a two-sided adhesive tape that was fixed to the sample support. Samples were coated with gold particles under vacuum condition and then were observed on a Quanta-200 scanning electron microscope (SEM, Quanta-200, FEI, Netherlands) for outer surface using an accelerating voltage of 5 kV. The accelerating voltage was 2.00 kV and the magnification range were from x 400 and x 945.
3. Results and discussion
7
Journal Pre-proof Sixty-seven flavouring compounds were identified and grouped into 8 different families:
hydrocarbon
monoterpenes,
oxygenated
monoterpenes,
hydrocarbon
sesquiterpenes, alcohols, aldehydes, ketones, furans, and C13-norisoprenoids (Table 1 – 4). In fresh sample, which was used as control, hydrocarbon monoterpenes and sesquiterpenes were by far the dominant groups accounting for 70.5 % and 29.0 % respectively, referred to the total volatile profile for fresh peel samples. At lower levels, aldehydes contributed 0.23 %, alcohols 0.12 %, oxygenated monoterpenes 0.05 %, ketones 0.08 % and furans and C13-norisoprenoids < 0.01 %.
3.1. Effect of drying methods on volatile composition of mango peels. 3.1.1. Monoterpenes and sesquiterpenes Hydrocarbon monoterpenes group was dominated by 3-carene in every sample (Table 1). This is in agreement with other authors who reported this compound as the major one in other mango cultivars such as Kent, Haden, Keitt, or Tommy Atkins (Andrade, Maia, & Zoghbi, 2000; Bonneau et al., 2016; Pino & Mesa, 2006). Beyond 3carene, great quantities of α-terpinolene, α-phellandrene, and D-Limonene were found. These compounds are regarded as key odorants due to their sensorial features described as citrus and resinous responsible for the typical mango-like aroma described in the literature (MacLeod & de Troconis, 1982). Nevertheless,
changes
occurred
during
treatments
to
hidrocarbonated
monoterpenes. In general, terms, almost all hidrocarbonated compounds decreased their amounts after the application of drying methods. Regards to the aforementioned compounds, lower losses were detected in those mango peels underwent to oven-dried at 45 ºC compared to the other two methods. This behaviour was also confirmed for practically all monoterpenes. In general terms, oven-drying at 45 ºC was the most
8
Journal Pre-proof respectful treatment as it caused a loss of 15.7 % compared to the fresh samples, not being a significant change according to the Student-Newman-Keuls test (α = 0.05). Oven drying at 60 ºC and freeze-drying caused significant higher losses of 59.7 % and 77.7 % respectively. This fact suggested that both high temperatures and vacuum conditions drove to hydrocarbon monoterpenes losses. Only two compounds, eucarvone and citral, were identified as oxygenated monoterpenes providing a total of 0.07 µg/gDM in fresh mango peel. Eucarvone seemed to be more stable versus heat treatments and freeze-drying conditions. Contrary, citral, the most abundant compound in this group, was almost not detected in freeze-dried mango peel samples. However, citral concentrations increased in the oven dried samples, especially in those submitted to 45 ºC (0.06 to 0.13 µg/gDM). This fact suggested the citral enhancement by continuous exposure to warm air as it was previously reported in the literature (Degenhardt et al., 2014). However, no references explaining the formation mechanism were found. On the other hand, hidrocarbonated sesquiterpenes group was led by trans-βcarylophyllene, β-selienene,D-cadinene, α-gurjunene and α-humulene compounds among others contributing with 44.20 µg/gDM in fresh samples. Every hidrocarbonated compound was affected in detriment by the treatments applied since losses of 59.3 78.9 % were originated. This fact was in good agreement with those data reported in mango pulp by other authors (Bonneau et al, 2016). Likely to the previous group, significant differences were found on sesquiterpene content between the drying treatments applied. The oven dried of mango peels at 45 ºC during 18 hours preserved better the overall composition of sesquiterpenes which seemed to be more prone to decrease under higher temperatures or vacuum conditions. 3.1.2. Alcohols, aldehydes and ketones
9
Journal Pre-proof Within alcohols group, it was difficult to find an overall tendency on how treatments affected the compounds belonging to this group. This fact may be explained because of the physico-chemical properties of alcohols. The already present alcohols in fresh samples are prone to evaporate under heat or freeze-drying treatments. Nevertheless, new ones could be generated as a result of hydrolysis reactions of glycosides compounds favoured by the temperatures applied during drying processes. This behaviour is already shown in the literature on mangoes samples (Bonneau et al., 2016) and other fruits (Franco et al., 2004). Even though total alcohols slightly increased due to the treatments, some clarifications should be pointed out. On the one hand, compounds such as (Z)-3-hexen-1-ol or 1-octanol decreased in the treated samples while on the other hand, similar compounds as 3-octanol and 2-ethyl-1-hexanol increased. As happened in the previous group, few differences can be found between the three treatments, especially between samples dried at 60 ºC and those submitted to freeze-drying. The thermal treatment using 45 ºC seemed to emphasize the appearance of alcohols. The reduction of these compounds when applying drying techniques could be counterbalanced through the release of alcohols present in their glycoside’s forms. Some of the aldehydes underwent an increase during the treatments. All the compounds detected from these groups were aliphatic aldehydes with the exception of benzaldehyde. It is particularly interesting to observe how the lyophilization process increased considerably the C6-aldehydes compounds such as hexanal (0.09 µg/gDM) and 2-hexenal (0.31 µg/gDM) compared to fresh samples (0.02 and 0.03 µg/gDM respectively). Aldehydes seem to be generated by oxidative and enzymatic reactions of fatty-acids amongst other causes (Belitz, Grosch, & Schieberle, 2009). Therefore, the increase of aldehydes observed in treated samples could be explained by this fact.
10
Journal Pre-proof A general tendency explaining the behaviour of ketones regarding drying treatments applied was not found (Table 3). Concentrations of 1-octen-3-one were increased significantly as consequence of the thermal treatments as occurred with 4octanol. Meanwhile, the quantities of 4-nonanone observed in fresh samples (0.10 µg/g) were drastically decreased in all treated peels until concentrations of 0.02 and 0.03 µg/g. Despite the significative differences found, the most respectful treatment was thermal drying using 45 ºC. 3.1.3. Furanic compounds and C13-norisoprenoids Furanic compounds such as 2-pentylfural and furfural were also identified in mango peels. There were no differences between fresh samples and freeze-dried one's regards to the total content of the aforementioned furanic compounds. However, their total amounts increased in mango peels submitted to both thermal treatments, 45 and 60 ºC.This fact was more remarkable for furfural whose concentrations were significantly increased, especially when the highest temperature was applied. This phenomenon might be explained by the different carbohydrates pathways degradation such as nonenzymatic reactions or even by enzymatic reactions or by the simple heating of sugars in acidic conditions. C13-norisoprenoids compounds such as β-damascenone and β-ionone were also detected. Despite low concentrations found in mango peels, they present an extremely low threshold detection, 0.002 and 0.007 ppb for β-damascenone and β-ionone respectively (Kennedy & Cosnett, 2002). Due to this fact, both compounds have previously pointed out as key contributors to the overall aroma profile of several cultivars of mango by their fruity-floral-violet-like aroma (Pino, 2012; Pino and Mesa, 2006; Pino et al., 2005).
11
Journal Pre-proof The concentrations of β-damascenone and β-ionone were enhanced by heat conditions and lead to the generation of these compounds. The same pattern has already reported in model studies and other fruit samples such as nectarines (Kashid et al., 2011; Sunthonvit, Srzednicki, & Craske, 2007). This fact seems to be attributable to the natural existence of these compounds in their glycosylated form whose hydrolysis catalized by enzymatic reactions and favoured by the temperature , could cause the release of their free forms (Skouroumounis & Sefton, 2000). This elucidation was in good agreement with other authors who also observed this C13-norisopreonids’ behaviour in other matrices (Sánchez-Palomo et al., 2009). Major quantities of these compounds (6.45 and 3.36 ng/g for β-damascenone and β-ionone respectively) were detected in those samples treated at 45 ºC suggesting that longer drying times favoured hydrolysis reactions.
3.2. Principal Component Analysis With the aim of highlighting the main changes in the volatile profile of mango peels due to the different drying methods applied, chemical data were submitted to a principal component analysis. The first two principal components explained nearly 81 % of the variance between the samples. Principal component 1 (PC1) explained almost 58 % of the variance. Figure 1 plots the samples on the coordinate grid defined by the first two principal components. PC1 separated fresh samples and those dried at 45 ºC from mango peels dried at 60 ºC and freeze-dried. A total of seventeen compounds contributed positively to the aforementioned separation (values ≥ 0.95) of the PC1 (Figure 2). They were primarily hidrocarbonated monoterpenes and sesquiterpenes such as isoterpinolene, γ-terpinene, trans-β-ocimene or α-humulene. These results showed the similarity between fresh samples and dried ones at 45 ºC.
12
Journal Pre-proof On the other hand, the principal component 2 (PC2) explained 23% of the variance and caused the graphical separation of fresh and freeze-dried mango peels from both oven dried samples (Figure 1). In the case of PC2, not only hidrocarboanted sesquiterpenes (aromadendrene and γ-muurolene) contributed positively to the discrimination but also did the hidrocarbonated monoterpene α-cubebene, and two aldehydes such as nonanal and octanal (Figure 2). Major concentrations of these compounds were detected in those samples not submitted to thermal treatments. Contrary, 4-octanol, which also was pointed out as a significant contributor to the differentiation among drying treatments, exhibited larger amounts in the mango peels which were submitted to oven heating.
Therefore, based on the results, the best drying method to stabilize and preserve the volatile composition of mango peels for its flavouring revalorization was the oven heating using low temperature, 45 ºC, during 18 hours. This evidence contrasts with data reported in bibliography in which freeze-drying is outlined as the most proper drying method to assurance the polyphenol and chlorophyll contents as well as the antioxidant activity of mango peels for its re-utilization as nutraceuticals or functional ingredients (Dorta, Lobo & González, 2012). Consequently, depending on the revalorization purposes, mango peels should be treated with the most suitable drying method.
3.3. Scanning Electron Microscopy (SEM) Images SEM images were obtained from each sample used in this technological study in order to observe morphological changes caused by the different treatments applied (Figure 3). In both fresh and freeze-dried samples, it washighly recognizable cell
13
Journal Pre-proof structure derived from the inner part of the peel which contained leftover pulp. In the case of the freeze-dried sample, cell structures seemed not to be damaged and inner parts of the cells appeared empty because of the sublimation (dehydration) process (Afonso et al., 2019). On the other hand, cell structures were not recognizable in oven dried mango peels.The leftover surface pulp disappeared in both samples as consequence of the thermal treatmentand spherical morphologies, related to pectins structure, were appreciated. The application of temperature for a considerable period of time seemed to result in demethoxylation of pectins which lead to the generation of such spherical structures as it was reported by other authors in guava fruit (Osorio, Carriazo, & Barbosa, 2011).
4. Conclusions The recovery and utilization of valuable compounds from mango peel byproduct as a natural flavouring agent have become an important aspect for its sustainable exploitation. Based on the results, the proposed process to reclaim the valuable flavors from mango peel is oven drying at 45 ºC during 18 hours. These conditions not only assure the stability of mango peel reducing the moisture content but also have been proven to be the best choice for the preservation of volatile compounds of fresh mango peel. From an industrial point of view, despite the longer drying times, the application of moderate temperature, 45 ºC, also entails
a reduction in the energy costs to carry out the
stabilization process at industrial level.
Acknowlegments:
14
Journal Pre-proof Authors
thank
to
the
financial
support
of
the
Project
(SBPLY/17/180501/000509) from Junta de Comunidades de Castilla-La Mancha. Authors also thank to the Ibero-American Program of Science and Technology for Development, CYTED (118RT0543). R. Oliver-Simancas thanks to University of Castilla-La Mancha for the predoctoral grant. Authors are also grateful to the Company “Grupo Empresarial La Caña” for the mangoes traceability assurance and for its compromise with the research group and with the R+D+i.
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Journal Pre-proof R. Oliver-Simancas: Investigation, validation, formal analysis, writing – original draft M.C. Díaz-Maroto: methodoloy, supervision M.S. Pérez-Coello: methodoloy, supervision M.E. Alañón: Conceptualization, writing – review and editing, visualization, project administration, funding acquisition, supervision.
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Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
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Figure 1. Graphical distribution of mango peel samples dried with different methods in comparison with fresh samples defined by PC1 and PC2 according to the PCA applied to volatile composition data.
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Figure 2. Loadings of the main contributors to discrimination among different drying methods applied to mango peels and fresh ones based on the principal component analysis of volatile composition.
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Figure 3. Scanning electron micrographs of fresh mango peel (FRESH), freeze-dried mango peel (FD), oven-dried mango peel at 45 ºC (D45) and oven-dried mango peel at 60 ºC (D60). The magnification was set as × 945 on FRESH and FD and x 400 on D45 and D60.
Journal Pre-proof Highlights
Mango peel is an natural source of odour-active compounds
Due to its high moisture, mango peel should be stabilised for its revalorisation
Drying methods should be optimized to avoid losses of volatile compounds
Oven drying at 45 ºC for 18 hours preserved better the chemical profile of mango peel
Journal Pre-proof Table 1. Hydrocarbonand oxygenated monoterpenes compounds detected in fresh and dried mango peel samples (µg/gDW, n = 3).
LRI
COMPOUNDS
FRESH MEAN
SD
DRIED AT 45 ºC MEAN
SD
DRIED AT 60 ºC MEAN
SD
FREEZE DRIED MEAN
SD
Hydrocarbon monoterpenes ---
α-Pinene
1030
α-Fenchene
1041
Camphene
1090
β-Pinene
1136
3-Carene
1153
α- Phellandrene
1166
o-Cymene
1169
α-Terpinene
1186
Sylvestrene
1188
D-Limonene
1200
β-phellandrene
1229
Cis-β-Ocimene
1235
α-Thujene
1240
ϒ-Terpinene
1246
Trans-β-Ocimene
1260
m-Cymene
1263
p-Cymene
1271
Isoterpinolene
1278
α-Terpinolene
1370
Trans-allo-ocymene
1427
o-Cymenene
1436
p-Cymenene
1457
α-Cubebene Hidrocarbonated monoterpenes
0.39 0.04 0.01 0.02 67.19 5.62 0.07 1.12 0.47 4.68 1.97 0.05 0.14 0.31 0.40 0.10 0.98 1.51 12.18 0.02 0.06 0.39 0.18 97.89
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.08b 0.00c 0.00c 0.00d 15.72b 0.47c 0.01b 0.23b 0.02d 0.98c 0.16c 0.00c 0.01c 0.03c 0.04d 0.01b 0.11c 0.09c 1.06d 0.00c 0.01 0.05b 0.03c 18.00b
0.37 0.04 0.01 0.01 61.33 3.95 0.08 0.87 0.35 3.31 1.48 0.03 0.10 0.21 0.20 0.10 0.98 0.96 8.51 0.02 0.07 0.35 0.06 83.38
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.08b 0.00c 0.00c 0.00c 5.86b 0.91b 0.00b 0.20b 0.07c 0.31b 0.31b 0.00b 0.01b 0.05b 0.02c 0.02b 0.06c 0.21b 1.10c 0.00b 0.01 0.02b 0.01b 8.13b
0.20 0.02 0.01 0.01 27.54 1.86 0.04 0.43 0.18 1.77 0.63 0.02 0.04 0.10 0.09 0.07 0.52 0.46 3.54 0.01 0.05 0.19 0.03 39.79
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.03a 0.00b 0.00b 0.00b 4.21a 0.12a 0.00a 0.02a 0.01b 0.28a 0.10a 0.00a 0.00a 0.02a 0.01b 0.00a 0.03b 0.09a 0.72b 0.00a 0.00 0.01a 0.00a 5.57a
0.13 0.01 0.00 0.01 16.37 0.89 0.04 0.24 0.11 1.02 0.38 0.01 0.03 0.06 0.04 0.06 0.37 0.22 1.69 0.01 0.06 0.16 0.17 22.07
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.02a 0.00a 0.00a 0.00a 3.20a 0.21a 0.00a 0.03a 0.01a 0.21a 0.08a 0.00a 0.01a 0.01a 0.01a 0.00a 0.03a 0.05a 0.43a 0.00a 0.00 0.03a 0.02c 4.28a
Oxygenated monoterpenes 1559
Eucarvone
1693
Citral Oxygenated monoterpenes
0.01 ± 0.00b 0.06 ± 0.00a 0.07 ± 0.00b
0.01 ± 0.00b 0.13 ± 0.00c 0.14 ± 0.00d
0.01 ± 0.00a 0.10 ± 0.01b 0.11 ± 0.01c
0.01 ± 0.00b ND 0.01 ± 0.00a
Values with different superscripts in the same row denoted significant differences according to the Student-Newman-Keuls test at p ˂ 0.05. Samples were defined according to the treatment applied: “Fresh”, no treatment applied; “Dried at 45 ºC”, oven dried at 45 for 18 h; “Dried at 60ºC”, oven dried at 60 ºC for 12h; “Freeze dried”, Freeze dried at -53.2 ºC and 1.1 x 10-2 mbar for 12 h.
Journal Pre-proof Table 2. Hydrocarbon sesquiterpenes compounds detected in fresh and dried mango peel samples (µg/gDW, n = 3)
LRI
COMPOUNDS
1492
α-Copaene
1532
α-Gurjunene
1541
β-Gurjunene
1576
Cis-β-Caryophyllene
1591
β-Elemene
1598
Trans-β-Caryophyllene
1608
Aromadendrene
1647
Alloaromadendrene
1649
Isocarilophyllene
1657
γ-Gurjunene
1670
α-Humulene
1677
γ-Selinene
1690
γ-Muurolene
1696
Viridiflorene
1712
Valencene (isomer I)
1716
Valencene (isomer II)
1721
β-Selinene
1725
α-Selinene
1758
D-Cadinene Hidrocarbonated sesquiterpenes
FRESH MEAN
3.85 5.24 0.16 0.25 0.05 11.94 0.14 0.59 0.26 0.23 4.10 0.16 0.28 0.88 0.33 0.23 7.65 1.09 6.77 44.20
SD
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.38c 0.24c 0.01d 0.03c 0.01b 3.12b 0.05c 0.05c 0.02d 0.01d 0.08d 0.05b 0.05b 0.09b 0.04b 0.04b 2.16c 0.16b 1.27b 6.56c
DRIED AT 45 ºC MEAN
1.78 1.89 0.06 0.16 0.02 4.93 0.03 0.26 0.13 0.08 2.77 0.13 0.10 0.24 0.20 0.12 4.35 0.50 0.26 18.00
SD
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.27b 0.36b 0.01c 0.01b 0.00a 0.38a 0.01a 0.02b 0.03c 0.02c 0.21c 0.01a,b 0.01a 0.02a 0.01a 0.01a 0.28b 0.02a 0.03a 1.19b
DRIED AT 60 ºC MEAN
1.42 1.34 0.04 0.08 0.01 3.14 0.02 0.16 0.08 0.05 1.71 0.09 0.06 0.18 0.14 0.08 2.62 0.29 0.28 11.79
SD
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.13b 0.06a 0.01b 0.00a 0.00a 0.50a 0.00a 0.03a 0.02b 0.00b 0.30b 0.03a,b 0.00a 0.02a 0.01a 0.01a 0.19a,b 0.04a 0.01a 0.90a,b
FREEZE DRIED MEAN
0.51 0.96 0.03 0.17 0.17 1.98 0.19 0.12 0.04 0.03 1.17 0.06 0.49 0.20 0.19 0.11 1.32 0.39 1.17 9.29
SD
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.11a 0.10a 0.00a 0.01b 0.01c 0.28a 0.02d 0.02a 0.01a 0.01a 0.19a 0.01a 0.08c 0.04a 0.08a 0.05a 0.16a 0.14a 0.19a 1.03a
Values with different superscripts in the same row denoted significant differences according to the Student-Newman-Keuls test at p ˂ 0.05. Samples were defined according to the treatment applied: “Fresh”, no treatment applied; “Dried at 45 ºC”, oven dried at 45 ºC for 18 h; “Dried at 60 ºC”, oven dried at 60 ºC for 12 h; “Freeze dried”, Freeze dried at -53.2 ºC and 1.1 x 10-2 mbar for 12 h.
Journal Pre-proof Table 3. Alcohols, aldehydes and ketones compounds detected in fresh and dried mango peel samples (µg/gDW, n = 3)
LRI
COMPOUNDS
FRESH MEAN
SD
DRIED AT 45 ºC MEAN
SD
DRIED AT 60 ºC MEAN
SD
FREEZE DRIED MEAN
SD
Alcohols 1387
4-Octanol
1390
(Z)-3-Hexen-1-ol
1399
3-Octanol
1496
2-Ethyl, 1-hexanol
1566
1-Octanol Alcohols
ND 0.10 ± 0.00c 0.01 ± 0.00a 0.01 ± 0.00a 0.04 ± 0.00b 0.16 ± 0.00a
0.01 0.04 0.16 0.03 0.02 0.27
± ± ± ± ± ±
0.00a 0.01b 0.02b 0.00b 0.00a 0.02c
0.01 0.01 0.16 0.02 0.02 0.22
± ± ± ± ± ±
0.00a 0.00a 0.02b 0.00b 0.00a 0.02b
ND 0.02 ± 0.00a 0.14 ± 0.00b 0.05 ± 0.01c 0.04 ± 0.00b 0.23 ± 0.01b
ND 0.02 ± 0.00a 0.02 ± 0.00a 0.03 ± 0.00a 0.04 ± 0.01a,b 0.11 ± 0.04b 0.02 ± 0.00a ND 0.06 ± 0.01a 0.01 ± 0.00a tr 0.32 ± 0.05a
0.04 0.05 0.02 0.26 0.03 0.04 0.07 0.04 0.10 0.01 0.01 0.67
± ± ± ± ± ± ± ± ± ± ± ±
0.01b 0.00c 0.00a 0.01c 0.01a 0.00a 0.00c 0.00b 0.01b 0.00 b 0.00b 0.03c
0.03 0.03 0.02 0.10 0.03 0.06 0.04 0.03 0.05 0.01 0.01 0.40
± ± ± ± ± ± ± ± ± ± ± ±
0.00a 0.01b 0.01a 0.01b 0.00a 0.00a 0.00b 0.00b 0.01a 0.00a 0.00a 0.03b
ND 0.09 ± 0.00d 0.08 ± 0.01b 0.31 ± 0.02d 0.05 ± 0.01b 0.15 ± 0.01c 0.03 ± 0.00a 0.01 ± 0.00a 0.05 ± 0.00a 0.01 ± 0.00a 0.01 ± 0.00a 0.80 ± 0.04d
0.01 ± 0.00a 0.10 ± 0.01b ND 0.11 ± 0.01d
0.05 0.03 0.01 0.09
± ± ± ±
0.00d 0.00a 0.00a 0.00c
0.03 0.02 0.01 0.06
± ± ± ±
0.00b 0.01a 0.00a 0.01b
0.01 0.03 0.02 0.05
Aldehydes ---
Pentanal
1065
Hexanal
1180
Heptanal
1215
2-Hexenal
1286
Octanal
1393
Nonanal
1430
2-Octenal-(E)
1465
2,4-Heptadienal
1499
Decanal
1522
Benzaldehyde
1537
2-Nonenal Aldehydes Ketones
1299
1-Octen-3-ona
1324
4-Nonanona
1337
5-Hepten-2-one, 6-methyl Ketones
± ± ± ±
0.00b 0.00a 0.00a 0.00a
Values with different superscripts in the same row denoted significant differences according to the Student-Newman-Keuls test at p ˂ 0.05. Samples were defined according to the treatment applied: “Fresh”, no treatment applied; “Dried at 45 ºC”, oven dried at 45 ºC for 18 h; “Dried at 60 ºC”, oven dried at 60 ºC for 12 h; “Freeze dried”, Freeze dried at -53.2 ºC and 1.1 x 10-2 mbar for 12 h.
Journal Pre-proof Table 4. Furanic and C13-norisoprenoids compounds detected in fresh and dried mango peel samples (ng/gDW, n = 3)
LRI
COMPOUNDS
FRESH MEAN
SD
DRYED AT 45 ºC MEAN
SD
DRYED AT 60 ºC MEAN
SD
FREEZE DRIED MEAN
SD
Furans 1226 1464
2-pentylfuran Furfural Furans
6.83 ± 0.69a,b 1.78 ± 0.09a 8.61 ± 0.69a
7.64 ± 0.19b 4.03 ± 0.39b 11.67 ± 0.56b
2.82 ± 0.10a ND 2.82 ± 0.10a
6.45 ± 0.52b 3.36 ± 0.26c 9.80 ± 0.48c
5.71 ± 0.48a 9.93 ± 1.09c 15.64 ± 0.62b
5.88 ± 0.76a 3.01 ± 0.24b 8.89 ± 0.67a
C13 norisoprenoids 1826
β-damascenone β-ionone C13 norisoprenoids
4.75 ± 1.77a,b 2.54 ± 0.28b 7.29 ± 1.58b
3.90 ± 0.34a 1.93 ± 0.41a 5.83 ± 0.63b
Values with different superscripts in the same row denoted significant differences according to the Student-Newman-Keuls test at p ˂ 0.05. Samples were defined according to the treatment applied: “Fresh”, no treatment applied; “Dried at 45 ºC”, oven dried at 45 ºC for 18 h; “Dried at 60 ºC”, oven dried at 60 ºC for 12 h; “Freeze dried”, Freeze dried at -53.2 ºC and 1.1 x 10-2 mbar for 12 h.