Effect of storage temperature and time on the microbial quality and sensory properties of extrudates produced from pearl millet (Pennisetum glaucum (L) Leake) and Bambara groundnut (Vigna subterranea) flour blends

Abstract

This study investigates the impact of storage conditions (temperature and time) on the microbial quality, moisture content, and sensory attributes of extruded puffed snacks formulated from blends of pearl millet flour and Bambara groundnut flour. Puffed snacks were prepared from seven flour blends made from pearl millet and Bambara groundnut in a proportion of 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, and 80:20, respectively, while 100% pearl millet and 100% Bambara groundnut flours were used as control. The extrudates were processed using a twin screw extruder, packed in aluminium laminate, and stored at two separate temperatures (28 ± 2 and 37 ± 2°C). After that, microbial analysis was conducted biweekly for 5 months, moisture content and sensory analysis were conducted once a month for four months and five months respectively. Our findings revealed an increase in total bacterial counts over the storage period, ranging from 1.00 to 6.84 CFU/g and 1.00–7.11 CFU/g at 28 and 37 °C, respectively. Fungal counts varied from 0.00 to 4.08 spores/g and 0.00–4.48 spores/g for snacks stored at 28 and 37 °C, respectively. The mean moisture gains for snacks stored at 28 and 37°C were 0.86 and 0.89%, respectively. Furthermore, the sensory parameters decreased as the storage period progressed, with the snacks' overall acceptability ratings increasing from 2.38 to 7.71 as the pearl millet percentage increased. Extruded samples M₉ (100% pearl millet) and M₈ (80% pearl millet and 20% Bambara groundnut) have the fewest bacterial counts, while samples M₁ (100% Bambara groundnut) and M₂ (20% pearl millet and 80% Bambara groundnut) have the least fungal counts. The sensory evaluation showed a preference for snack M₉ followed by snack M₈. The findings of this study will offer valuable insights to the food industry regarding storage strategies aimed at improving the safety and sensory attributes of products made from pearl millet and Bambara groundnut.