Development of Probiotic Finger Millet (Eleusine coracana) Milk Powder

Abstract

Milk and its products contain all the essential nutrients for daily nutrition. The milk is generally from an animal source. Due to the high cost involved in the upkeeping of dairy animals and various issues related to sustainable milk sourcing, the food industry is looking for alternative milk sources. Also, dairy-based milk products are less acceptable nowadays due to their association with various health issues such as high cholesterol, casein allergy, and lactose intolerance. Plant-based milk products, rich in essential nutrients, polyphenols, and phytochemicals, could be a potential solution to address these issues. As of now, soy and oat-based milk are available on the market. However, the nutritional quality and stability of these products are not satisfactory. Finger millet, an underutilized crop, could be explored as a source of milk and further value-addition. Finger millet is rich in antinutrients such as tannins and phytates that reduce the digestibility and chelates minerals. The current work was to develop a process protocol for producing probiotic finger millet milk powder. Finger millet was hydrated with ultrasound treatment to reduce the processing time and antinutrient content. Milk was extracted from the ultrasound-hydrated finger millet and then fermented with Lactiplantibacillus plantarum (MCC 2974). The fermented milk was spray-dried to encapsulate the probiotics in the finger millet milk powder. The process was optimized at every step to have reduced processing time, lesser antinutrients, maximum resistance starch, improved probiotic cell viability, and better powder quality. During hydration, an ultrasound amplitude of 66 %, treatment time of 26 min, and a grain-to-water ratio of 1:3 resulted in the best desirable parameters with a reduction in phytate and tannin contents of the finger millet by 66.98 and 62.83%, respectively. In-vitro digestion showed the presence of improved resistant starch. Increased crystallinity in XRD analysis also confirmed the presence of improved resistant starch. The fermented milk from the ultrasound hydrated finger millet showed higher cell viability (8.16±0.02 log CFU/ml), as confirmed by CLSM and FTIR analysis. The probiotic finger millet milk sample showed higher resistance in terms of cell viability (4.64±0.03 log CFU/ml) during in vitro digestion conditions. The optimum spray drying condition could be achieved at 151.50 °C inlet temperature, 29.52% maltodextrin content, and 100 ml/h feed rate. A probiotic finger millet milk powder was characterized by its various quality and morphological characteristics. Powder flow properties, phytochemical properties, and proximate composition of probiotic finger millet milk powder were in an acceptable range. SEM images of the developed powder showed higher cell viability. XRD pattern of the powder showed the amorphous structure with partial crystallinity of the particles confirming the higher shelf life. The probiotic powder stored at 25°C and 4°C exhibited 35 days and 56 days of shelf life, respectively, with the recommended probiotic viability of 6 log CFU/g. A laminated aluminium pouch with good moisture barrier properties was suitable packaging material to store probiotic powder. During moisture sorption kinetics, the Peleg model was best fitted for the sorption isotherm study. The sensorial properties of the developed probiotic finger millet milk powder showed good consumer acceptance. The cost of production of probiotic finger millet milk powder in the laboratory setup was ₹ 11.97 INR per gram.