Effects of thermosonication on the nutritional and sensory quality of NFC orange juice during storage at low temperature

Not from concentrate (NFC) orange juice is processed directly from the fresh orange after cleaning, sterilized and aseptically filled, because it does not go through the process of concentration, reduction and preparation, so as to maintain the original flavor and nutrition of the fruit. Sterilization is the most significant processing step in juice production, which can effectively prolong the shelf life of citrus juice through killing microorganisms. Generally, pasteurization is a kind of widely used thermal sterilization techniques in the industry and is also widely used in the manufacture of liquid foods. However, high temperatures inevitably have some negative effects, such as causing deterioration of color and even odor, changing the physicochemical properties, and reducing the heat-sensitive nutritional and functional components in the juice, which may be detrimental to the health of consumers. Therefore, there is an urgent need to systematically compare the influences of different sterilizations on the quality of NFC orange juice and select suitable sterilization methods for processing high-quality NFC juice. Thermosonication (TS) technology, as a low heat sterilization technology, has been widely concerned in the sterilization of liquid food. In order to evaluate the efficiency of TS on the quality of NFC orange juice, the effects of TS (600 W, 60 ℃, 13 min) on the microorganisms, color, limonin, nomilin, vitamin C, total phenol, total flavonoid content and antioxidant activity of NFC orange juice were investigated during storage at low temperature for 35 days compared to the traditional pasteurization (70 ℃, 15 min), and the changes in volatile compounds of NFC orange juice with traditional pasteurization and TS were also analyzed by GC-MS. The results showed that both treatments effectively ensured the microbiological safety of NFC orange juice during storage. The sugar and acid components of NFC orange juice were stable during storage, and TS treatment did not affect the taste of NFC orange juice. Compared with the traditional pasteurization group of NFC orange juice, TS treatment improved the turbidity stability of orange juice. With the extension of storage time, TS treatment increased the L*, a* and b* values. However, the ΔE* values were all less than 1.00, the color difference could not be perceived, and the BI value decreased by 12.50%-16.67%. The loss rate of Vc in NFC orange juice was reduced by 10.52% of TS group. The contents of total phenol and total flavone of TS group were 1.00-1.06 times of those in the traditional pasteurization group. The limonin content decreased by 17.37%-56.62% and nomilin content decreased by 9.32%-63.85%, respectively. The DPPH free radical scavenging ability and FRAP total antioxidant capacity were 1.09-1.21 times and 1.11-1.70 times that of pasteurization, respectively. GC-MS analysis identified 49 volatile compounds. The traditional pasteurization process produced 1-octene-3-ol, 2-octene-1-ol, 2-octyne-1-ol, ethyl butyrate, (E)-2-octenal, (E)-2-nonenal, (E)-2-heptenal, creinaldehyde, 6-methyl-5-heptene-2-ketone and butyric acid in the NFC orange juice, which were the mainly volatile components that caused the hot odor of NFC orange juice, but TS effectively inhibited to produce these volatile components in NFC orange juice, thus avoiding the hot odor of the juice. Therefore, TS was better than traditional pasteurization for preserving the nutritional and sensory quality of NFC orange juice. It was suggested that TS might be a promised and alternative sterilization for NFC orange juice. The research can provide theoretical basis and technical parameters for further improving TS application of NFC orange juice.