In vitro carbohydrate digestibility tests in the Indian white shrimp, Penaeus indicus
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Paper chromatography was used to determine the capacity of wild Penaeus indicus digestive gland homogenates to hydrolyse 27 carbohydrates containing a variety of bond types. Whereas all α-1 → 4 and α-1 → 1 bond oligosaccharides (including disaccharides and Schardinger β-dextrin) and α-D-glucans like starch, glycogen and pullulan were hydrolysed to a great extent, the same bond in the α-D-galacturonan pectin only underwent limited hydrolysis while that in the heteroglycan alginic acid was not broken down at all. β-type glycosidic bonds tended to be resistant to enzymatic degradation. The β-2 → 1 bond in inulin and the β-2 → 6 bond in levan as well as the β-1 → 4 bond in β-D glucans like cellulose, xylan, chitin and agar were not hydrolysed. However, β-D-glucans with β-1 → 3 linear bonds like laminarin and laminaritol were hydrolysed. There was also some breakdown of salacin. Among simple carbohydrates, chitin building units (β-1 → 4 bonds) were not hydrolysed indicating the absence of endogenous and exogenous (microbial) chitobiase. In contrast, the same bond type in cellobiose and lactose as well as the β-2 → 1 bond in sucrose were hydrolysed. These results indicate the absence of β-1 → 4 glucanases but the presence of significant activities of β-disaccharases except chitobiase. The carbohydrate component of any diet formulation for shrimp should therefore be assessed in light of these findings. The simple paper chromatography procedure employed requires minimum investment and can be used by any small scale shrimp feed manufacturing unit or shrimp farm.