Use of high-pressure processing and low-temperature storage to extend the performance shelf life of 2 types of string cheese.

The manufacturing method of string cheese is similar to mozzarella, but the hot curd is extruded through narrow tubes or pipes, which align the protein fibers that provide the characteristic ability for consumers to pull strings from this cheese. Firmness is another important performance attribute for consumers who just bite into the string cheese without peeling off strings. There have only been a few studies on string cheese, but it is known that stringiness and firmness decrease during prolonged storage, which is a particular challenge for exporting string cheese. We explored 2 treatments to try to retain the stringiness and firmness of string cheese for longer storage periods. The techniques used were high-pressure processing (HPP; 600 MPa for 3 min) and reduced storage temperature (0°C). In other cheese varieties, these techniques have helped extend the performance shelf life. We tested these techniques using the 2 main types of commercial string cheese: direct acid string cheese (DASC) and cultured string cheese (CSC), which were obtained from 2 different manufacturing facilities. The DASC had higher fat (∼2.2%) and higher pH values (∼0.2 units) compared with the CSC. The CSC had higher protein content (∼3.4%), higher insoluble calcium content (∼8 mg insoluble Ca/g protein) and higher texture profile analysis (TPA) hardness values (∼4 N) compared with the DASC. Due to the compositional differences, the 2 varieties were statistically analyzed separately for all other attributes. In both cheese types, HPP caused an immediate reduction in stringiness, some solubilization of insoluble calcium, and a slight increase in the cheese pH values. High-pressure processing also caused a slight increase in TPA hardness of the CSC samples until 14 d (possibly due to a slight increase in cheese pH). The use of the 0°C storage temperature reduced proteolysis and helped retain firmness during storage. Low-temperature storage could help extend the performance shelf life of string cheese by a couple of months, but HPP was not suitable, as the process caused an immediate reduction in stringiness due to the disruption of the matrix induced by the HPP treatment.

Physicochemical changes in fresh-cut wax apple (Syzygium samarangenese [Blume] Merrill & L.M. Perry) during storage.

Physicochemical changes, such as peel and flesh colours, total anthocyanin content, browning index, firmness, total soluble solid (TSS), titratable acidity (TA), sugar acid ratio (TSS/TA), antioxidant capacity, total phenolic content and ascorbic acid content, in fresh-cut Taaptimjan wax apple fruit stored at 4±2°C and 12±2°C for 7days were investigated. The skin of fresh-cut fruit stored at 4±2°C showed higher a(∗) value, chroma and total anthocyanin content and lower hue angle than those stored at 12±2°C. Lightness (L(∗) value) and whiteness index of the fresh-cut fruit flesh stored at 12±2°C showed significantly lower than those stored at 4±2°C which related to an significant increase in browning index. Firmness, total soluble solid, titratable acidity and sugar acid ratio did not significant changes during storage. Antioxidant capacity and total phenolic content increased throughout storage. Ascorbic acid content of the fresh-cut fruit stored at 4±2°C remained constant throughout storage whilst ascorbic content at 12±2°C decreased and was lower than that at 4±2°C. At 4±2°C antioxidant capacity and ascorbic acid content were higher than that stored at 12±2°C whilst there was no significant difference in total phenolic content. In conclusion, the reduction of whiteness index and the increase in browning index of fresh-cut wax apple flesh were the key factors affecting its quality and storage at 4±2°C could reduce the change in the flesh colour and maintained the peel colour and nutritional values of fresh-cut wax apple fruit during storage.