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BACKGROUND Flavor loss is a common problem when manufacturing apple juice and is closely related to the properties of the colloidal pectin particles in cloudy juice. The flavor changes and particle properties of three varieties of apple juice (‘Ralls’, ‘Golden Delicious’ and ‘Fuji’) during processing were investigated. RESULTS Compared with manually pressed juice, juice made by industrial pulping and filtration contained larger particles, resulting in the ‘sweet and sour’ taste of the juice being relatively weak and the diversity of aromas narrower, as determined by E‐nose analysis. Pulping and filtration, however, released some important flavor esters, such as butyl butyrate, hexyl‐2‐methyl butyrate, and hexyl butyrate. The transformation of volatile compounds during apple juice processing was closely related to the apple cultivar but, in all three varieties, the content of 1‐hexanal and (E)‐2‐hexenal in the juice gradually decreased during processing. Pectinase treatment reduced the colloid particle size and increased the ζ‐potential of the juice, resulting in better uniformity and stability, as well as increasing the content of nonanal. After pasteurization, the colloidal particles tended to aggregate and the ζ‐potential decreased. Many volatile compounds decreased in concentration or disappeared after heat treatment. CONCLUSION The flavor and colloidal properties of cloudy apple juice changed markedly during processing and the effect of each processing step was different. © 2020 Society of Chemical Industry

The high pressure homogenization (HPH) process is a non-thermal technology that can be used to change the structure of fluid foods. Appropriate HPH treatment is benefit for uniform particle sizes distribution in juice and reducing pulp sedimentation. Cloudy apple juice was used as the experimental material in this study to evaluate the homogeneous pressure and homogeneous times (10-1, 10-2, 20-1, 20-2, 30-1, 30-2, 40-1, 40-2, 50-1, 50-2) on stabilities of juice. The indicators, such as, cloud value, cloudy stability, particle size distribution, ζ-potential and dynamic instability were investigated for juice stability. The results showed that, when homogenization at 20 Mpa for one time, the apple juice showed lower cloud value, higher cloudy stability, more uniform particle sizes, higher ζ-potential and lower dynamic instability. Therefore, the better HPH condition on stability of cloudy apple juice was 20 Mpa homogenizing for one time.

The effect of interactions between polyphenolic substances (Chlorogenic acid, epicatechin and gallic acid) and gliadin under different pH (pH 3.8/7.0) were analyzed by fluorescence spectrum. The results showed that adding polyphenols could induce static fluorescence quenching of gliadin solution at pH 3.8 and 7.0. Fluorescence quenching spectrum of chlorogenic acid-gliadin complex at pH 3.8 presented a red shift toward long wave, while other phenols spectra showed blue shifts toward the short wave. The binding ability showed a significant difference between acid condition and neutral condition, and the quenching constants (Kq and KSV) of all three polyphenols at pH 3.8 were lager than pH 7.0. Compared to epicatechin and gallic acid, pH value had a marked effect on binding ability of chlorogenic acid with gliadin.