Evaluation of thermal and non-thermal processing effect on non-prebiotic and prebiotic acerola juices using 1H qNMR and GC–MS coupled to chemometrics
Introduction
Acerola (Malpighia emarginata DC.) is a valuable fruit for human diet and a potential source of Vitamin C (ascorbic acid). Acerola juice presents an appreciated flavor and a pleasant color. The insertion of prebiotic compounds as soluble dietary fiber has been reported as a way to improve the beneficial effects of fruit juices for human healthy (Araújo et al., 2015, da Silva et al., 2014). Prebiotics are non-digestible carbohydrates that reach the intestine where they selective stimulate the growth of the gut microbiota associated with health benefits. The insertion of prebiotic compounds helps significantly to improve the functional efficacy of probiotic fruit juices. Among the prebiotic compounds, inulin and other non-digestible gluco-oligosaccharides are considered important for health reducing risks of certain diseases (Tingirikari, Gomes, & Rodrigues, 2017).
Thermal processing is the standard industrial process to increase the shelf life of commercial fruit pulps and juices. Ultra High Temperature (UHT) is an efficient thermal processing for foodstuffs sterilization (Soares et al., 2017, Sucupira et al., 2017). However, nutritional changes in functional composition, vitamins, and other nutrients are usually reported for thermal processing. Therefore, new non-thermal processing technologies as cold plasma and ultrasound have been widely studied for inactivation of enzymes, microorganisms, besides minimizing the loss food quality nutritional value (Misra, Keener, Bourke, Mosnier, & Cullen, 2014).
The knowledge of the compounds affected by the food processing is an important part of the food products development. The composition of food might influence on flavor, aroma, color, stability, and microbial control of the final product. Among the analytical techniques, Nuclear Magnetic Resonance (NMR) spectroscopy allows the compounds assignment in food matrices as a whole (without previously chemical separation or purification). Untarget sample exploration, processing effect evaluation, characterization of the genotype of the fruit; evaluation of the environmental factors and different agronomical practices (irrigation condition, solar incidence, altitude and others) in the product quality are NMR useful applications (D’Imperio et al., 2007, da Silva et al., 2016, Spraul et al., 2009). Additionally, the Gas Chromatography coupled to Mass Spectrometry (GC–MS) is widely used to characterize the aroma composition of fruits juices (Alves Filho et al., 2017, Bicas et al., 2011). However, due to complex and extensive datasets obtained for food matrices, chemometric analyses are often necessary for a proper analytical evaluation, especially in untargeted analysis.
Pure and prebiotic acerola juice (juice containing inulin or gluco-oligosaccharides) samples were processed by High Temperature Short Time (HSTS); Ultra High Temperature Sterilization (UHT) and non-thermal processing (ultrasound and plasma). After processing, NMR spectroscopy and GC–MS (both combined with chemometrics) were used to detect possible chemical changes in the acerola juice samples composition.
Section snippets
Raw material
The raw material used was non-pasteurized and free of preservatives acerola (Malpighia emarginata DC) frozen pulp purchased from a local producer (KIPOLPA™, Fortaleza-CE, Brazil). The product was kept frozen (−18 °C) until the processing. Initially, the pulp was diluted (1:2) with potable water. Three different juices were used for the thermal and non-thermal processing: pure juice (PJ); juice with the addition of inulin (JI); and juice containing gluco-oligosaccharides (JGO). The pure juice
Results and discussion
The oligosaccharides formation in acerola juice detected by TLC showed gluco-oligosaccharides with a degree of polymerization up to 7. The present study evaluated three samples of acerola juice (pure juice, juice with the addition of inulin, and juice with gluco-oligosaccharides) using NMR, HPLC-UV, and GC–MS. The results were presented separately according to the analytical technique.
Conclusion
Both thermal processing (HTST and UHT) had a pronounced effect on the juices composition compared to non-thermal processing considering the primary metabolites (NMR) and volatile profile (GC–MS). The chemometric results of the NMR data demonstrated that some of the organic compounds found in the processed juices, as carbohydrates and malic acid, are altered according to the type of processing – thermal or non-thermal. The both non-thermal processing did not present significant effect on acerola
Conflict of interest
The authors declare no conflict of interest.
Acknowledgements
The authors thank CNPq, Brazil (465335/2014-4) and FUNCAP, Brazil (DCR-0024-01686.01.00/15) for the financial support and the award of scholarship (303791/2016-0).
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