Abstract
Apple juice that is designated 'Not from concentrated' (NFC) is now increasingly popular with consumers due to its unique taste and rich nutritional value. However, layered precipitation and instability have emerged as serious technical problems that restrict the viability of the NFC apple juice industry. This study researched the influence of water-cored 'Fuji' apple fruit storage under different temperatures (0, 20 °C) and times (0, 9, 18, 30, 60 days) on the turbidity stability of NFC apple juice. Changes in the physicochemical properties (juice yield, pH, total soluble solids and titratable acid), turbidity stability (turbidity and particle size) and precipitation sensitive substances (insoluble starch, total phenolics, soluble protein and pectin) of NFC apple juice were determined, combined with the respiratory rates and ethylene release of apples, in order to study post-harvest regulation and control of processed fruit. Results indicated that fruit storage temperature and time significantly guided the turbidity stability of NFC apple juice. As a typical respiratory climacteric fruit, apple fruit stored 45 days at 0 °C and 15 days at 20 °C gained the best juice stability, respectively. This is basically consistent with the respiratory peak of fruit when processing raw materials. During the post-ripening process, the insoluble starch in apple gradually hydrolyzed into fructose and glucose, while total phenolics diminished and water-soluble pectin content increased. On the other hand, the amounts of pectin, soluble protein and phenolics in fruit juice declined as the fruit aged in the late storage period (stored 75 days at 0 °C and 40 days at 20 °C). Meanwhile particle size became larger and the turbidity stability of cloudy juices also decreased. This study's results will provide a sound theoretical basis for improving the turbidity stability of NFC apple juice by regulating the physiological state of processed raw materials.