EFFECT OF SOY PROTEIN ISOLATE ON QUALITY OF BISCUIT FROM MALTED PEARL MILLET FLOUR

Abstract

ABSTRACT Plant based proteins such as soy protein isolate (SPI) are replacing traditional animal proteins in foods due to increased desire for high protein, nutritious and healthy diets. Pearl millet is a climate smart cereal crop rich in resistant starches, minerals, dietary fibre and phenolic compounds that contribute to the quality of its final food products. Malted pearl millet flour is characterised by reduced anti-nutrients in addition to improved nutritional properties, compared to the un-malted flour. The study’s main objective was to determine the effect of SPI on the quality of biscuit produced from malted pearl millet flour (MPM). Simplex lattice mixture design for two component mixtures were used to investigate the effect of flour combination (70-90% MPM; 10-30% SPI) on the nutritional and sensory quality of biscuits. MPM-SPI biscuits were analysed for proximate composition, physical properties and consumer acceptability. Data were analysed using ANOVA, regression model generation, and numerical optimisation. Quality of optimised MPM-SPI biscuit analysed were proximate composition, anti-nutrients, minerals, amino acid profile, protein digestibility, texture profile and sensory descriptive profile. Texture profile and consumer acceptability of optimised MPM-SPI biscuit and market reference biscuits (Coaster® biscuit and Digestive fibre® active biscuit were compared. MPM-SPI biscuits differed significantly (p<0.05) in moisture (8.36-12.60%), protein (9.69-20.02%), fat (8.15-14.17%), ash (2.64-3.59%), fibre (5.83-10.68%), and carbohydrates (48.82-54.27%) contents. The biscuits also differed significantly (p<0.05) in diameter (4.35-4.55 cm), thickness (0.61-0.73 cm), spread ratio (6.16-7.37), weight (5.16-5.78 g), browning index (19.08-23.27) and overall consumer acceptability (5.59-6.90). optimised biscuit (78% MPM and 22% SPI) had a desirability factor of 0.57. The quality of optimised MPM-SPI biscuit were moisture (7.53%), protein (15.15%), fat (10.32%), ash (3.20%), fibre (7.32%), carbohydrate (56.46%), phytate (9.71 mg/100g), tannins (0.04 mg/100g), iron (11.52 mg/g), zinc (3.86 mg/g), magnesium (81.71 mg/g), essential amino acids [valine (3.65 µmol/L), threonine (3.09 µmol/L), isoleucine (4.18 µmol/L), leucine (6.74 µmol/L), lysine (3.81 µmol/L), methionine (1.29 µmol/L), phenylalanine (4.46 µmol/L), histidine (2.39 µmol/L), tryptophan (0.87 µmol/L), glutamic acid (11.57 µmol/L)] and non-essential amino acids [glycine (3.39 µmol/L), alanine (4.64 µmol/L), serine (4.13 µmol/L), proline (4.39 µmol/L), aspartate (9.40 µmol/L), arginine (5.37 µmol/L), tyrosine (3.61 µmol/L), cysteine (1.34 µmol/L)] .Texture profile of optimised MPM-SPI biscuit had higher values for stringiness (2.49 mm), gumminess (4312 mm), adhesiveness (8.32 J), springiness (0.89), chewiness (3877 N) and cohesiveness (0.60) compared to reference biscuits. Although Coaster® biscuit had the highest (7.91) consumer acceptability, optimised MPM-SPI biscuit (6.88) was not significantly (p>0.05) different from Digestive fibre® active biscuit (6.80). Optimised MPM-SPI biscuit was described by high sensory intensities for dark and grainy appearance, brown colour, sweet taste, gritty, crunchy and hard texture, malty aroma and baked flavour. The optimum ratio of 78% MPM and 22% SPI are recommended for commercial production of biscuits due to its high protein content, good amino acid profile, low anti-nutrients, high mineral content and consumer acceptability.