Study On Reasons For Cloud Loss Of Huyou Juice And Influence Of Uhph On Its Stability

As a unique citrus variety, Changshan-huyou has high fruit yield, good quality, and has been well received by the majority of consumers in China. However, the processing of huyou fruit has a very low percentage, with a small amount of whole fruit drinks and preserved fruit products for the market. Currently, huyou fruit has still been mainly fresh saled, but in recent years, as the area under cultivation expanded and the production raised in a large extent, it is needed to find a new way for the outlet of the adequate and cheap raw materials. Simultaneously, compared with the clarified juice, consumers tend to choose cloudy juice because of its better sensory quality (such as flavor, texture and color, et al.) and nutritional value. Therefore, the development of cloudy huyou juice not only has the advantage of utilizing raw materials, but also has a regional market advantage. However, the stability of the cloudy juice is worse than that of the clarified juice. After a certain period of storage, it is easy to precipitate and separate into layers, which influences the juice consumption. In order to provide the theoretical and technical foundation for industrialized production of huyou cloud juice, and provide a reference for ultra-high pressure homogenization(UHPH) technology on popularization and application in the food industry, we studied in this work the reasons for the cloud loss in huyou juice, analyzed the impact and possible mechanism of UHPH on pectinesterase(PME) activity in huyou juice and the cloud stability of the juice, and investigated the influence of UHPH on the nutrition and shelf stability of huyou juice. The results were as follows:(1) The composition of huyou juice cloud was investigated. The effects of PME activity in juice, addition of PME、acid protease and pectinase, storage temperature on the cloud stability of huyou juice were studied. The results showed that huyou juice cloud mainly consisted of pectin and protein. The lower PME activity in huyou juice, the longer the turbidity of the juice remained, and the more stable the juice was. The presence of PME activity in huyou juice was one of the main factors of cloud loss. Acid protease could partially reduce the turbidity of the huyou juice, but the variation was not significant (P>0.05). Pectinase could significantly reduce the turbidity of huyou juice, resulting in cloud loss. The turbidity of huyou juice was getting lower with the increasing storage temperature. Ambient temperature storage was unbeneficial for the cloud stability of huyou juice.(2) Influence of UHPH in addition to the temperature factor on the cloud stability and physical and chemical properties of huyou juice was investigated. The effects of UHPH on the cloud stability of huyou juice and possible mechanism were discussed. The results showed that PME activity in huyou juice decreased with increasing homogenization pressure, and the turbidity increased as homogenization pressure increased. Centrifugal sedimentation rate was reduced with increasing homogenization pressure.120and more than120MPa UHPH could commendably prevent huyou juice from layering, but there was no obvious correlation between the suspended substance content and homogenization pressure. The viscosity of huyou juice treated by UHPH was higher than that of the control, but the differences between each treatment group tended to be no significance. After UHPH treatment, the average particle diameter of huyou juice was significantly reduced (P<0.05) and the particle size distribution range became narrow, and both of them continued to reduce with the homogenization pressure increased and the time prolonged. Due to the larger particles in the huyou juice sedimentation down gradually, both of the average particle diameter and the particle size distribution range were reduced with the time prolonged during storage. The greater the homogeneous pressure was, the smaller the layering speed was, and the more stable the system was.(3) Changes of Vc, pH, total soluble solid(TSS), color, titratable acidity, reducing sugar, pectin and soluble protein content before and after UHPH treatment and during low temperature storage were investigated. The impact mechanism of UHPH on huyou juice’s nutrition and shelflife stability were discussed. The results showed that UHPH treatment could result in a slow loss of Vc in huyou juice during storage, but the differences between the treatment groups was not significant (P>0.05), and Vc content decreased with prolonging storage time. UHPH had no significant effect on reducing sugar content, with a trend of decrease first and then increase following a decrease again during storage. UHPH could significantly increase pectin content in huyou juice(P<0.05) because of it making cell disruption and releasing pectin substances, and pectin content increased with increasing homogenization pressure, however, the difference between120and160MPa UHPH treatment groups was not significant (P>0.05), and pectin content in the juice decreased with prolonging storage time. Because of making cell disruption and releasing the soluble protein, UHPH could also improve the soluble protein content in huyou juice with a trend of increasing with increasing homogenization pressure and decreasing with prolonged storage time. Different pressure in UHPH treatments had no significant effect on TSS and titratable acid content of huyou juice, and TSS and titratable acid content changed slightly and remained stable during storage. After UHPH, the brightness of the juice increased, and yellowness and greenness strengthened. All of the brightness, yellowness and greenness declined in the early days of storage, but the color remained stable during the half and late period of storage.