Dry-heat processing at different conditions impact the nutritional composition and in vitro starch and protein digestibility of immature rice-based products.

Kulwa F Miraji,Anita R Linnemann,Edoardo Capuano,Henry S Laswai,Vincenzo Fogliano

doi:10.1039/d1fo01240a

Abstract

Immature grain represents a precious nutritional source in many rural Africa areas. To optimize processing of immature rice into pepeta (a traditional rice-flakes produced from immature rice grains), immature rice (TXD306 variety) harvested at 18 and 26 days after 50% heading were processed in the laboratory under different soaking (0 and 12 h) and roasting temperature (80, 100 and 120 °C) regimes. Riboflavin, nicotinic acid, nicotinamide and iron concentration increased with severity of roasting temperature, while thiamine has an opposite trend. Heating promoted the transformation of insoluble into soluble dietary fiber, increased lipid digestibility decreasing protein one, which showed the highest value when rice was roasted at 100 °C. Soaking before roasting significantly increased moisture and iron content while slightly increased riboflavin, nicotinic acid and nicotinamide when compared to unsoaked products. Among roasted products, starch digestibility increased with roasting temperature. Microstructure analysis indicated a complete loss of cell wall integrity in cooked rice, determining a complete starch and protein digestion while this is delayed in raw rice and roasted products. We concluded that roasting at 100 °C is the optimum temperature to produce pepeta of the highest protein digestibility and low starch digestibility. Soaking before roasting at 120 °C is best when retaining micronutrients is considered.

Highlights

Consumption of immature cereal-based products is common in communities where cereals are staple food
This study explored the effect of processing conditions to optimize the nutritional quality and digestibility properties of immature cereal-based products such as pepeta, a processed immature rice flake typically consumed in Tanzania
The dietary fiber transformation from insoluble to soluble fiber was linked with an increase in roasting temperature, showing pepeta processing technology can enhance fiber functionality of immature ricebased products

Summary

Introduction

Consumption of immature cereal-based products is common in communities where cereals are staple food. Firik ( known as frikeh or frekeh or freekah) is a scorched/roasted immature whole wheat-based food consumed in Arabic countries in the Middle East and Northern Africa.[1,2,3,4] Breads prepared from green maize and sorghum kernels are widely consumed in sub-Saharan Africa.[5] In Tanzania, pepeta, a locally prepared rice flakes from immature grains, is common among rice consuming communities.[6,7] Currently, consumption of immature cereal-based products is gaining popularity worldwide due to their nutritional and health potential benefits compared to fully mature cereal grains. This makes it impossible to guarantee a consistently good quality pepeta product and hinders its upscaling to the industrial production level

Methods

Results

Conclusion