The quality of boiled cassava roots: instrumental characterization and relationship with physicochemical properties and sensorial properties

Abstract

The physicochemical properties of twenty promising new improved cassava cultivars (13 sweet and 7 bitter), harvested at maturity in Benin, were assessed. In parallel, instrumental measurements and sensorial tests were performed to assess boiled cassava quality. These properties and physicochemical properties were tentatively correlated. The colour score of boiled cassava tuber was closely correlated with ΔE measured on fresh pulp, while mealiness (or friability) could be assessed by resistance to penetration, measured on cooked tuber slices. Mealiness could also be predicted from starch functional properties (such as apparent viscosity after pasting), cyanide potential and the water content of fresh tubers. The cassava tubers had a narrow amylose content range (18.2%–22.6% starch basis). In addition, bitter cultivars appeared to be quite homogeneous with, in particular, high sugar and protein contents but low fibre contents. They also had original starch functional properties, with high solubility and low paste viscosity.

Introduction

Cassava (Manihot esculenta, Crantz) is one of the most important root crops in tropical countries. In Benin, production has multiplied almost fivefold in the last 20 years, reaching an estimated 2 million tons in 1997 (FAO, 1997). Cassava roots are consumed in Benin in several forms, including boiled in water, roasted, fried or after conversion into intermediate products, such as gari, flour (from dried chips), tapioca or starch. Boiled cassava (fingnin dida) is one of the most common forms of consumption in both rural and urban areas. It is prepared by peeling, cutting and boiling fresh cassava roots. The main quality attributes of boiled cassava are whiteness, sweetness and friability, all of which should be high.

The sensory quality of cassava roots is an important factor for the acceptance of new improved cultivars by farmers (Safo-Kantaka, Boampong, & Asante, 2002). It is also one of the major reasons for the use of a harmful bitter cultivar in Malawi, as farmers there believe that bitter cultivars give a whiter flour and a less elastic stiff porridge (Chiwona-Karltun et al., 1995). However, although some publications deal with variation in starch quality with cultivar and age of plant (Defloor, Dehing, & Delcour, 1998; Eggleston, Omoaka, & Arowshegbe, 1993; Moorthy & Ramanujam, 1986) particularly with a view to industrial use, very little is known about the cultivar effect on the quality of traditional dishes prepared from cassava roots. Studies by Wheatley and Gomez (1985) and Asaoka, Blanshard, and Rickard (1991) showed an effect of both cultivar and age at harvesting on the organoleptic properties (taste and texture) of boiled cassava pieces from four cultivars. However, they were unable to find any relationship between organoleptic quality and the physicochemical characteristics of tubers or starch and concluded that further data on cassava root quality were required.

More data are available on the texture of boiled potato, particularly with regard to its friability (or mealiness), the principal sensory attribute of boiled potato tuber (Unrau & Nylund, 1957). It is generally held that tuber friability is due to cell rupture on chewing (Warren & Woodman, 1974). Several authors have related potato friability to starch content or starch properties. Starch swells during boiling, inducing a distension of the cell wall which facilitates cell separation in mealy potatoes (McComber, Osman, & Lohnes, 1988). However, no clear correlation has been found between starch content or starch properties and potato friability (McComber et al., 1988; Warren & Woodman, 1974) and other authors have hypothesized that friability should also or primarily be linked to cell wall properties (Iritani, Powers, Hudson, & Weller, 1977; Nonaka, 1980).

The aim of this paper is to assess the organoleptic properties of boiled cassava roots from 20 promising new improved cultivars harvested at maturity in Benin, to develop instrumental tests than can be routinely used to screen cassava cultivars for root quality, and to attempt to relate the sensory qualities of cassava roots to their physicochemical properties.