Microbial Shelf-Life, Starch Physicochemical Properties, and in Vitro Digestibility of Pigeon Pea Milk Altered by High Pressure Processing

This study examined the effects of high-pressure processing (HPP) on microbial shelf-life, starch contents, and starch gelatinization characteristics of pigeon pea milk. HPP at 200 MPa/240 s, 400 MPa/210 s, and 600 MPa/150 s reduced the count of Escherichia coli O157:H7 in pigeon pea milk by more than 5 log CFU/mL. During the subsequent 21-day refrigerated storage period, the same level of microbial safety was achieved in both HPP-treated and high-temperature short-time (HTST)-pasteurized pigeon pea milk. Differential scanning calorimetry and scanning electron microscope revealed that HPP at 600 MPa and HTST caused a higher degree of gelatinization in pigeon pea milk, with enthalpy of gelatinization (∆H) being undetectable for both treatments. In contrast, HPP at 400 MPa led to an increase in the onset temperature, peak temperature, and conclusion temperature, and a decrease in ∆H, with gelatinization percentages only reaching 18.4%. Results of an in vitro digestibility experiment indicate that maximum resistant starch and slowly digestible starch contents as well as a decreased glycemic index were achieved with HPP at 400 MPa. These results demonstrate that HPP not only prolongs the shelf-life of pigeon pea milk but also alters the structural characteristics of starches and enhances the nutritional value.