Comparative effects of thermal, high hydrostatic pressure, and UV-C processing on the quality, nutritional attributes, and inactivation of escherichia coli, salmonella, and listeria introduced into tiger nut milk

Abstract

Tiger nut milk is a low-acid health beverage that is marketed with the claims of being high in protein, monounsaturated fatty acid (oleic acid), fiber, starch, and minerals, in addition to vitamins C and E. In this study, the effect of nonthermal processing with UV light (UV-C) or high hydrostatic pressure (HHP) on the nutritive content (protein, vitamin C, polyphenols, and antioxidant), and quality characteristics (viscosity and color) of tiger nut milk were compared with thermal processing. Baseline studies established the treatments parameters to support a ≥5-log CFU reduction of Escherichia coli P36, Listeria innocua ATCC 51742, and Salmonella Typhimurium WG49 introduced into tiger nut milk and then treated with thermal or nonthermal methods. The thermal treatment at 608C for 30 min, HHP at 500 MPa for 120 s, and UV-C at 45.2 mJ cm-2 were required to achieve the target 5-log reduction. Thermal treatment resulted in a significant loss (P < 0.05) of total protein (34.9%), total phenolic content (28.7%), and vitamin C (27.1%) and negatively affected the tiger nut milk color, along with decreasing its viscosity. In contrast, HHP and UV-C light treatment retained protein and antioxidant content in tiger nut milk with no significant (P < 0.05) color change being recorded. Therefore, from a processing prospective, either UV-C light or HHP could be used to treat tiger nut milk, although additional hurdles to control the potential outgrowth of Clostridium botulinum during storage would be required. HIGHLIGHTS • Thermal and nonthermal methods can support a 5-log CFU reduction of model bacteria introduced into tiger nut milk. • Thermal treatment of tiger nut milk results in significant loss of protein, antioxidants, and quality properties. • HHP or UV-C treatment of tiger nut milk retains quality and nutritional characteristics. • HHP or UV-C are suitable for the pasteurization of tiger nut milk.