The effect of high hydrostatic pressure on the microbiological quality and physicochemical properties of lotus root during refrigerated storage

Abstract

Lotus root (Nelumbo nucifera Gaertn), an aquatic vegetable in China, is widely consumed due to its unique sensory and nutritional properties. However, fresh lotus root tends to deteriorate during storage. The aim of the study was to evaluate the effect of high hydrostatic pressure (HHP) on microbiological quality and physicochemical properties of lotus root. Lotus root was processed at HHP ranging from 300 to 600 MPa for 2.5 min to 25 min. The inactivation curves of natural microorganisms in lotus root by HHP were well fitted with the Weibull model. According to the inactivation of microorganisms, lotus root was subjected to 400 MPa for 10 min, 500 MPa for 5 min and 600 MPa for 2.5 min. The changes of microbiological quality and physicochemical properties (color, texture, pH and yield) were analyzed during three months of storage at 4 °C. The results showed that lotus root processed by 600 MPa exhibited a better microbiological stability than those of other treatments. The total plate counts (TPC) in lotus root treated with thermal processing, 400 and 500 MPa were 5.20, 5.12 and 4.36 log10 CFU/g, respectively on 45th day. The growth of microorganisms caused the increase in △E, decrease in hardness and pH in other treatments. Treatments of 600 MPa for 2.5 min had little effect on color during storage. There were no significant changes in the L⁎, a⁎ and b⁎ values (p > 0.05). The hardness of lotus root treated with 600 MPa decreased by 34.22% after 90 days. The pH value of lotus root with 600-MPa treatment remained statistically constant during 90-day storage. After 90 days, lotus root processed by 600 MPa retained 88.04% of its weight. These results indicated that HHP at 600 MPa for 2.5 min was an efficient non-thermal alternative for extended shelf-life of lotus root. As an interesting alternative to traditional processing method, high hydrostatic pressure processing has the potential to produce high quality foods. This research provides information of storage stability of lotus root after HHP and thermal processing. The available data are provided for the evaluation and application of HHP in lotus root, and criteria for commercial production of high quality lotus root with safety requirements could be established.