Fat replacers have been developed to produce low-calorie foods due to the association of fat-rich diet to lifestyle diseases. Teff (an underutilized and under-researched cereal), and maize starch pastes modified with stearic acid could be used as fat replacers because of their reduced gelling ability and higher viscosity. The effect of teff and maize starch pastes modified with stearic acid on the rheological properties, microstructure, freeze-thaw and high temperature stability of lowcalorie mayonnaise type emulsions (LCMTE) was investigated. Starch suspensions (10% w/v) containing stearic acid (1.5%) were pasted for an extended holding time (2 hr at 91 °C) in a Rapid Visco Analyzer (RVA) and used to prepare LCMTE with 50% and 80% oil replacement.LCMTE with modified teff and maize starches had lower yield stress and viscosity and larger oil droplets compared to LCMTE with unmodified teff and maize starches. Increasing oil replacement level (50% to 80%) increased the viscosity. LCMTE with maize starch had higher yield stress and viscosity and smaller oil droplets than LCMTE with teff starch. All samples showed shear thinning behaviour (n < 1). All the LCMTE were more stable to freeze-thaw cycles and high temperature storage than full fat mayonnaise. At 50% oil replacement, unmodified and modified teff and maize starch with stearic acid could produce LCMTE. When the oil content was further decreased to 80% only the LCMTE with modified starches were similar to the full fat.
This study investigates the formation and properties of compatible binary colloidal blends between pre-gelatinized (uncomplexed and complexed with stearic acid) maize starches (hydrophilic component) and commercial zein (hydrophobic component) with the aim of creating a bipolymeric material with unique properties. The blends were formed under alkaline condition (0.1 M NaOH) with 3:1, 1:1 and 1:3 starch: zein (w/w) ratios. The 3:1 starch-zein blends showed best stability or compatibility. Blends made with starch complexed with stearic acid had better stability than those with uncomplexed starch. Most of the blends were not freezethaw stable except for 3:1 starch (complexed with stearic acid)-zein blend. The blends with better stability had higher apparent viscosity, and a microstructure showing uniform mix of starch -zein as observed by confocal laser scanning microscopy. The likely reason for the compatibility of starch and zein is the change in surface activity of zein, possibly due to deamidation, in 0.1 M NaOH as shown by the negative zeta potential values. The pre-gelatinized maize starches also show negative zeta potential values. In conclusion, compatible binary colloidal blends can be produced between pre-gelatinized maize starch and commercial zein using 0.1 M NaOH.
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