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For the first time in literature, this study revealed the participation of polymeric components of orange juice cloud and pulp (such as proteins, arabinogalactan proteins, or protein-pectin complexes) during nonenzymatic browning. In a quest to better understand the non-enzymatic browning of shelf-stable orange juice during storage, the juice was fractionated into different fractions depending on the solubility in water/ethanol and the obtained fractions were characterized. The results showed that brown compounds formed during storage of orange juice distributed over water insoluble (pulp), ethanol insoluble (cloud), and ethanol soluble (serum) fractions. In the ethanol insoluble fraction, the brown compounds are hypothesized to be associated with proteins, arabinogalactan proteins and/or protein-pectin complexes of this fraction without significantly changing their molecular weight distribution, monosaccharide composition, and protein content. The changes in the ethanol soluble fraction including ascorbic acid degradation, acid-catalyzed hydrolysis of sucrose, and formation of furfural and 5-hydroxymethylfurfural were highly correlated to the browning development of the juice during storage.

Although natural structural barriers are factors limiting nutrient bioaccessibility, their specific role in anthocyanin bioaccessibility is still unknown. To better understand how natural barriers govern bioactive compound bioaccessibility, an experimental approach comparing anthocyanins and carotenoids was designed, using a single plant matrix. Initial results revealed increased anthocyanin bioaccessibility in masticated black carrot. To explain this observation, samples with increasing levels of bioencapsulation (free-compound, homogenized-puree, puree) were examined. While carotenoid bioaccessibility was inversely proportional to the level of bioencapsulation, barrier disruption did not increase anthocyanin bioaccessibility. This means that mechanical processing is of particular importance in the case of carotenoid bioaccessibility. While micelle incorporation is the limiting factor for carotenoid bioaccessibility, anthocyanin degradation under alkaline conditions in the gastrointestinal tract dominates. In the absence of structural barriers, anthocyanin bioaccessibility is greater than that of carotenoids.

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Nonenzymatic browning during storage of pasteurized shelf-stable orange juice causes a major color deterioration which negatively affects consumer acceptance of the juice. This study, for the first time, investigated on a kinetic basis the effect of pH and suspected nonenzymatic browning reaction precursors such as ascorbic acid, fructose, and arginine on nonenzymatic browning during accelerated storage (42 °C) using an orange juice based model system. The results showed that lowering the pH of the model juice system from 3.8 to 1.5 significantly increased the rate of ascorbic acid degradation, the rate changes (increases and decreases) in different sugars, and the rate of furfural and 5-hydroxymethylfurfural formation. These changes coincided with a higher browning intensity which became more pronounced towards the end of storage of the juice model system. Similarly, adding more ascorbic acid and fructose largely increased the formation of furfural and 5-hydroxymethylfurfural, respectively, and resulted in a higher browning intensity. In conclusion, lowering the pH of the orange juice or addition of ascorbic acid or fructose will enhance its browning during prolonged storage.

clmt/lmt/ Highlights  Defining shelf-life dates should rely on scientific rather than trial-and-error methods. New approach and future challenges to study shelf-stable food quality changes during storage are reviewed. Integrated science-based approach as useful tool for quality investigation and shelf-life prediction. Shelf-life may be estimated from kinetics combined with consumer acceptance limits.

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