Development of biscuits using purple rice flour, defatted green-lipped mussel powder and spices

Biscuits are the most popular bakery food consumed worldwide. The nutritional values of biscuits can be fortified by adjusting their formulations. Wheat flour is one of the main ingredients in a biscuit mix and biscuits can be fortified by using alternative flours containing a high nutritional value, such as Thai purple rice (Oryza sativa L.) flour. However, this has seldom been used in bakery products, i.e. bread or biscuits. Defatted green-lipped mussel powder (Perna canaliculus) is a by-product, which is a good source of protein to add to biscuits. Spices tend to give the biscuits a nice smell and taste, particularly in biscuits where defatted green-lipped mussel powder (P. canaliculus) has been added to the recipe to increase the protein content. Wheat-purple rice biscuits (50:50) supplemented with defatted mussel powder at 0-20%, together with spices, were evaluated by measuring their proximate compositions, physical characteristics and antioxidant contents along with their liking scores as derived from a standard tasting trial. This study was carried out in 5 stages: 1) substituting a portion of wheat flour with Thai purple rice flour, 2) producing biscuits from different flour mixtures, 3) incorporating defatted mussel powder to the biscuits containing purple rice flour, 4) using spices in the formulation of biscuits with defatted mussel powder, 5) studying changes in the quality of biscuits containing defatted mussel powder and spices during storage for four months. An increase in substitution levels of purple rice flour increased the level of dietary fibre from 2.3 to 5.6% and protein digestibility from 24.8 to 66.46%, and decreased the predicted glycaemic index (pGI) from 63.1 to 48.6 compared to refined wheat flour. Lower amounts of rapidly digested starch with higher slowly digested starch contents were found in whole flour made from purple rice with a 75% substitution of purple rice flour for wheat flour. In addition, antioxidant compounds (total phenolic compounds, anthocyanin and total flavonoid) and antioxidant activity significantly increased (P < 0.05) in the substituted flour compared to the refined wheat flour. The wheat-purple rice biscuits contained high fibre contents (4.1%) with small only changes in physical properties. The biscuits also showed positive characteristics using in vitro digestibility methods. The lowest pGI was found in the 100% purple rice flour biscuits. The change in colour of the biscuits was due to the antioxidant compounds from the purple rice flour. The total phenolics, anthocyanin and flavonoid contents of the fortified biscuits ranged from 0.8-3.0 mg gallic acid equivalents/100 g dry weight (DW), anthocyanins 9.4-51.5 mg/kg DW and flavonoids 0.6-1.3 mg catechin equivalents/100 g DW, respectively. Sensory evaluation revealed that panellists liked the 50% substitution level of purple rice flour for wheat flour in the biscuit mix compared to the 75% and 100% substitution levels. The highest crude protein level (11.3%) with the highest protein digestibility (83.5%) was found in the 20% defatted mussel powder biscuits mixed with ginger and galangal compared to biscuits enriched with 10% and 15% defatted mussel powder. The antioxidant compounds and antioxidant activity also significantly increased (P < 0.05), and the total starch contents decreased, when increased amounts of protein from defatted mussel powder were incorporated into the biscuit mix. Overall, the supplementation of 10% defatted mussel powder was accepted by all the ethnic groups with a higher score given than for the 20% supplemented biscuits. Pacific Islanders appreciated the mussel-supplemented biscuits more than the other three ethnic groups, Caucasian, Chinese and Thai. The fortified biscuits enriched with defatted mussel powder and spices contained higher protein (26.4%), fibre (52.9%) and ash (6.0%) contents with a lower fat (5.6%) content compared to the wheat-purple rice biscuits (50:50). The in vitro starch digestibility and pGI decreased in the fortified biscuits by 19% and 6.2%, respectively, while the protein digestibility increased by 3.7%, corresponding to the increased levels of defatted mussel powder present. The inclusion of defatted mussel powder at 15% showed no significant differences in liking scores in terms of colour and overall appearance; whereas, the flavour and overall acceptability scores were significantly lower than the control biscuits from 7.0 to 4.6 and from 7.4 to 5.3, respectively. Storage of the 15% defatted mussel biscuits at 21.6 ± 0.4°C and 34.2 ± 0.1°C in two different packaging types (polyethylene terephthalate, PET and aluminium foil laminate, AL) for 12 weeks showed small reductions in antioxidant compounds and antioxidant activity (P < 0.05), but no changes were observed in the colour and physical parameters. Overall, substitution of purple rice flour can be used as an alternative flour in terms of functional properties to produce a good texture in biscuits with a higher antioxidant potential and lower predicted glycaemic index. Spices can be successfully incorporated into mussel-containing biscuits to improve the overall taste of the biscuits. A combination of lower temperature (21.6 ± 0.4°C) and AL pouches proved to be the best storage condition for biscuits giving, overall, acceptable rates of free fatty acid and peroxide values even after storage for 12 weeks