Sensory and physicochemical characterization of selected aromatic rice types in Ghana

Abstract

Rice forms a major part of the Ghanaian diet, yet locally produced rice is not patronized as it should. This study was designed to characterize locally grown aromatic rice varieties based on their physico-chemical and sensory properties to provide data needed for quality improvement and enhance market competitiveness. A preliminary survey of 390 consumers in Accra was conducted to ascertain consumer perceptions, knowledge and preferences for aromatic rice. The physicochemical and sensory characteristics of four locally grown aromatic rice varieties (Ex-Baika, Ex-Hohoe, Jasmine 85 and Marshall), and two popular imported brands (Royal Feast and Sultana) were assessed. The physical characteristics of the raw milled rice, proximate and mineral composition; as well as the functional properties of flour from the rice varieties were evaluated. Sensory texture and sensory flavour profiling were also carried out on the rice samples and the consumer acceptability of the different rice samples was also determined. Cluster observation analysis was used to determine varieties with similar characteristics while principal component analysis (PCA) was used for pattern recognition and display. The survey results showed poor availability of the local aromatic rice. Consumer knowledge of such rice was therefore limited. The imported aromatic rice was, however, more available and therefore popular. The domestic varieties had higher width values (2.21-2.26mm), 1000-Grain Weight (19.5-22.3g) and densities (0.87- 0.91g/ml) than the imported brands. Physical parameters that negatively impact on quality [i.e. brokens (13.6-32.7%), moldiness (0.89-2.23%), chalkiness (0.17-0.44%) and immature grains (0.05-0.33%)] were also higher. The local varieties were nutritionally superior to the imported ones in terms of their mineral composition. All the samples were non-waxy with high gelatinization temperatures, (low alkali spreading scores of 1.0-2.17), soft gels (66-98mm) and low to intermediate amylose (15.9 – 22.7%) rices. The imported brands cooked faster and were less sticky with high lengthwise expansion, but the local varieties were associated with high amylose content, water uptake, peak viscosities and retrogradation. On cooking, the imported rice brands had better aroma, cooked grain flavour, sweetness and firmness that positively impacted the overall acceptability of these brands. On the other hand, the local varieties were more associated with starchiness, stickiness, adhesiveness and cohesiveness of mass. These sensory characteristics negatively predicted consumer acceptance of cooked rice but are desirable for rice dishes requiring grains to stick together. Cooked rice aroma of rice was the most important factor determining consumer acceptance of aromatic rice ahead of appearance and colour of the rice. The findings from this study will be relevant to rice breeders and processors in breeding programmes in terms of grain quality improvement and selection of rice with desirable characteristics