S. N. Moorthy

Effect of pretreatment of fresh Amorphophallus paeoniifolius on physicochemical properties of starch

Fresh roots of Amorphophallus paeoniifolius were separately pretreated with sodium hexametaphosphate (SHMP), potassium metabisulphite (KMS), sodium chloride (NaCl), and ammonium hydroxide (NH4OH) within a range of 1–5% (w/v) concentration and glyceryl monostearate (GMS) at 0.025–0.125% concentration. The quality of starch extracted from pretreated roots was compared with that obtained from fresh roots by direct aqueous extraction. The starch samples prepared from chemically pretreated roots showed characteristic changes in properties of water soluble amylose content, swelling and solubility and α-amylase susceptibility. X-ray diffraction of starch samples from chemically pretreated roots although resembled that of control, there was noticeable shift with respect to their ‘d’ spacing and Io/Imax values.

Physicochemical and enzyme susceptibility characteristics of starch extracted from chemically pretreated Xanthosoma sagitifolium roots

Fresh samples of Xanthosoma sagitifolium were pretreated with sodium hexametaphosphate (SHMP), potassium metabisulphite (KMS), sodium chloride (NaCl) and aqueous ammonia, all in a concentration range of 1-5 % (w/v), and with glyceryl monostearate (GMS) at 0.025–0.125 % concentrations. The properties of these pretreated samples were compared with those of the control obtained by direct water extraction. The properties of the starch pretreated with chemicals showed characteristic changes regarding amylose contents, especially soluble amylose, and lipid extractability. Starch samples prepared from fresh roots pretreated with sodium chloride displayed a lower amylase digestibility. Control starch samples and the one prepared from roots pretreated with 5 % aqueous ammonia showed the highest amylase activity at 20 min incubation time. Other experimental samples showed only marginal changes.

Textural and Gelatinization Characteristics of White, Cream, and Orange Fleshed Sweet Potato Tubers (Ipomoea Batatas L.)

Sweet potato is an important food crop having nutritive value in terms of starch, carotein, and minerals. The acceptability and overall quality of the products depend on their textural and rheological attributes. Cooking quality of the tubers could be related to the textural, pasting, and gelatinization properties, which vary depending on the flesh color of the tubers. Also, being a promising ingredient in many of the traditional and industrial products, the physico-chemical and functional properties of sweet potato flour are very much important for their selection for developing various value added products. The textural, gelatinization, and pasting characteristics of white, cream, and orange fleshed sweet potato tubers were analyzed and their thermal softening behavior was modeled by linear regression and fractional conversion techniques. Significant variations were observed in the properties among different varieties (p < 0.05). Kinetics of texture degradation on cooking were explained by first-order and dual-mechanism first-order models and the latter was found to be more suitable. The first three principal components explained about 85% of the total variation in texture profile parameters, gelatinization, and pasting properties. Though there was no similarity in the textural properties of the raw tubers among the varieties of same flesh color group, the quality of the cooked tubers and flours of different varieties in the same group are similar as revealed by the multivariate analysis.

Functionality of Tuber Starches

Abstract Root and tuber crops form an important part of the diet in many tropical belts and are rich in starch; cassava and sweet potato being widely used for starch extraction. Unlike cereal starches, these starches show a wide range of property and are hence used in food and industry. Modified starches from these crops are becoming more important. Until recently, only cassava and sweet potato starches were studied in detail, but of late, the other tuber starches have been subjected to lot of investigations. In this chapter, extraction, properties, uses, and modifications have been described in detail. Among the physicochemical properties, granule size and shape and structural properties studied by XRD and molecular analysis, amylose content, and structure are very diverse among the starches. Wide variation in swelling characteristics and solubility patterns and thermal properties determined by differential scanning calorimetry indicates not only the effect of origin but also the environmental and processing conditions. Viscosity, pasting, and rheological features also exhibit a similar trend. Digestibility, another important attribute in food applications, has been investigated in detail. Various modifications—physical, chemical, and enzymatic—have been carried out on these starches to suit to different applications and discussed.