INFLUENCE OF GRAPEFRUIT DIETARY FIBRE RICH POWDER ON THE RHEOLOGICAL CHARACTERISTICS OF WHEAT FLOUR DOUGH AND ON BISCUIT QUALITY

Dietary fibre rich powder obtained from grapefruit by-products was analysed for its chemical composition and functional properties. The results revealed that grapefruit powder contained 50.39% of total dietary fibre, 17.36% of pectin substances, 6.65% of proteins, and 2.77% of fats. Grapefruit powder also exhibited good hydration properties (water holding, water retention, and swelling capacity), whereas its fat absorption capacity and emulsifying activity were very low. The effect of grapefruit powder as partial substitution of wheat flour in biscuit making (substitution levels 5, 10, and 15%) on the farinographic properties of wheat dough, physical characteristics, and sensory parameters of produced biscuits were also investigated. It was observed that increasing the level of grapefruit powder in dough increased water absorption and dough development time, while dough stability and mixing tolerance index decreased. Physical characteristics of biscuits (specific volume, volume index, width, thickness, and spread ratio) significantly decreased with the increasing level of grapefruit powder in biscuits. Biscuits containing 5% of grapefruit powder were the most acceptable for assessors, higher levels of grapefruit powder in biscuits negatively affected overall acceptance presumably due to the high intensity of bitter taste and increased hardness of biscuits.