Stabilisation and Characterisation of a Peanut Based Ready to Use Supplementary Food (RUSF)

ABSTRACT

The prevalence of under nutrition in many communities requires the need for the availability of nutrient dense affordable food supplements such as Ready-to-use supplementary foods. An energy dense, drinkable ready to use supplementary food produced by enzyme hydrolysis of cooked mixture of peanuts, cowpeas and rice with added vitamin mineral mix was both acceptable to consumers and showed promise of efficacy in improving the nutritional status of women of child bearing age through nutritional intervention studies. However the product was physically, chemically and microbiologically unstable, and did not store for long at ambient temperatures. This work was done to improve the physical and microbiological stability of the drinkable peanut based ready-to-use supplementary food.

Roasted peanut, cooked cowpeas and rice were mixed in a ratio of 3:3:4 (dmb) and slurried in a colloid mill, hydrolysed with alpha-amylase and bromelain enzymes at 50 ̊C and 43 ̊C respectively to obtain a liquefied product of about 20% solids. Calculated amounts of vitamin and mineral mix were added to meet the requirements of the target population for the supplement. The product was thermally processed by either pasteurizing (10, 20 and 30 minutes) at 95 ̊C or retorting at 119 ̊C for 10 minutes. The effectiveness of the thermal processes on the microbial and chemical stability of the product was monitored at 25, 35 and 45 ̊C for five weeks. The flow behaviour of the product and viscosity were characterised using the Brookfield digital viscometer. The effects of particle size on product separation rate were determined, and the application of stabilizers (CMC, carrageenan and Xanthan gum) to modify product viscosity examined. The shelf life of the product was calculated based on chemical deterioration rate by modelling free fatty acids data on Arrhenius kinetics.

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The finer particles in the product (≤106μ) had faster settling rates than the larger ones (≥300 and 500μ). The apparent viscosity of the product was 440cP, and generally increased by the use of stabilizers. Addition of Xanthan gum at 1% level gave the greatest increase in apparent viscosity (1111.0 cP), and its subsequent application in the product formulation substantially reduced the settling rate of particles, and provided some measure of physical stability to the product.

Optimal starch hydrolysis was achieved after 1 hour incubation with alpha amylase at 50 ̊C- 55 ̊C. Protein hydrolysis by bromelain was highest at 43 ̊C, and SDS-PAGE zymograms showed extensive hydrolysis of all proteins within I hour of incubation with bromelain. Prolonged incubation times led to reformation of peptides as was noticeable on the zymograms of 3 hour hydrolysates, suggesting that plastein-like reactions probably occurred under the conditions of incubation with bromelain.

Microbiological stabilization of the product by thermal processing proved inadequate as was evidenced by high microbial counts in all treatments. Heat penetration data from both pasteurization and sterilization processes showed that thermal processing was inadequate to assure microbial stability of the product. Accelerated shelf life studies (based on lipid oxidation data) showed the product to be chemically stable at room temperature (25 ̊C) for 22 days. Practically however, the product shelf stability did not go beyond three days at ambient conditions due to microbial spoilage.

While it was possible to improve the physical stability of the product, microbiological stability was not attainable using physical treatments, and other options need to be explored. It is essential to improve the shelf life of the product at ambient temperature storage, in order to enhance its distribution and usage among the rural poor and undernourished who need it the most.