Effects of superheated steam processing on the functional properties of oat groat, bran and flour, and on viability of Geobacillus stearothermophilus spores

In this work, superheated steam (SS) processing was evaluated as a method of heat treatment alternative to conventional processing of oats. The effects of SS on the physicochemical and functional properties of oat groats and/or flour and bran fractions were determined using: (a) mixed Canadian oat cultivars (typically used for commercial processing); (b) two oat cultivars varying in physical grain characteristics and composition (i.e. beta-glucan content). Additionally, the viability of heat-resistant Geobacillus stearothermophilus ATCC 10149 spores challenged with SS was determined and modelled mathematically.;The functional properties of oat groat, as well as flour and bran fractions obtained from groats of Furlong and HiFi cultivars processed with SS (at 110, 120, and 130°C) were similar or better than those obtained via the conventional process. Compared to the conventional heat treatment, the processing with SS significantly (P<0.05) decreased groat hardness but increased cold paste viscosity of flour and bran slurries. Generally, the effects of different heat treatments applied to groats on the functional properties of groats, flour, and bran fractions were augmented by the different chemical composition (mainly differences in the content and solubility of beta-glucans) of the two oat genotypes tested. The size of groats (within each cultivar) significantly (P<0.05) affected groat hardness, but it appeared to have lesser influence on the physicochemical properties of flour and bran fractions. Among the four heat treatments examined (conventional and SS at 110, 120, and 130°C treatments), the SS treatment at 110°C appeared to have the most positive effects on the physicochemical properties (increased molecular weight and viscosity in solution) of beta-glucans isolated from the bran fractions of Furlong and HiFi. It appeared that the treatments of groats with SS at 120 and 130°C caused partial depolymerization of BG (lower molecular weights) thereby increasing their solubility, compared to the control heat treatment and the treatment with SS at 110°C. Subsequently, the apparent viscosities of aqueous solutions of BG obtained from samples treated with SS at 120 and 130°C were lower than those obtained from the samples control heat-treated and SS processed at 110°C.;Treatment of Geobacillus stearothermophilus spores with SS temperature of 105°C was initially (first 5 min of treatment) more effective than SS treatments at 130 and 145°C. Treatments with SS at very high temperatures (160 and 175°C) effectively reduced viability of G. stearothermophilus spores. An interruption of SS treatments at 105, 130, and 145°C by brief cooling intervals also effectively reduced the spore viability. The spore response to SS treatments at 105-175°C depended on inoculum size. A mean z-value of 25.4°C was calculated for the spores at low and high inoculum levels (3 and 6 log 10 colony forming units per gram, cfu/g, respectively) challenged with SS at 130-175°C.;Tailing was observed in survivor curves of G. stearothermophilus spores challenged with SS. The survivor curves were described best by the Weibull model, a non-linear regression model. The Weibull model was expanded by describing its parameters (alpha, beta) as a function of SS temperature for the range of 130-175°C. This allowed accurate predictions of the spore survival ratios based on the SS temperature and processing time only (with the exception of predictions for spores at high inoculum level challenged with SS at 130°C). The Weibull model is recommended to describe and to model inactivation of G. stearothermophilus spores with SS at high temperatures (145-175°C). (Abstract shortened by UMI.);Oat groats processed with SS at temperatures of 110-130°C had acceptable moisture content, appearance, and exhibited cold paste (64°C) viscosity higher (by up to 1,200 cP) than that of conventionally processed oat grain. The use of SS at temperatures of 140-160°C for processing of groats resulted in even higher cold paste viscosity but also caused low final moisture content (4-7% wet basis, wb) and fast development of rancidity. Processing with SS was effective in the inactivation of peroxidase in groats in which post-processing moisture content was at 10% (wb) and less. The optimum conditions for SS processing of oat groats were: temperature of 110°C, a velocity of 1.00 m/s, and processing times of 10 and 14 min, both of which gave shelf stable groats with moisture content at the safe storage limit and cold paste viscosity significantly (P<0.05) higher than that of the conventionally processed oat groats.