Protein digestion in penaeid shrimp: digestive proteinases, proteinase inhibitors and feed digestibility

Abstract

Protein is the most abundant ingredient in both natural and prepared diets of penaeid shrimp. The assessment of protein digestion through the developmental stages of penaeids may contribute to the development of more suitable feeding schedules for their cultivation. Among the techniques to study protein digestion, detection and characterization of digestive proteinase inhibitors in proteinaceous feed ingredients can be achieved by substrate-[sodium dodecyl sulphate polyacrylamide gel electrophoresis] (SDS-PAGE). In vitro assays of protein digestibility are also useful tools when testing alternative protein sources in the formulation of shrimp feeds. The present article reviews three methods that have been used to assess protein digestion: (1) detection and characterization of proteinase activity and proteinaceous proteinase inhibitors by substrate-SDS-PAGE, (2) quantification of proteinase activity, and (3) in vitro evaluation of digestibility of dietary protein sources by shrimp proteinases. A compilation of previously reported and unpublished data on some aspects of penaeid protein digestion is presented. Trypsin activity of Litopenaeus schmitti varied considerably during larval and postlarval development, showing the highest value at protozoea III. The molecular weight of digestive proteinases from early stages of Farfantepenaeus paulensis also differed from the adult pattern, and some activity bands could be characterized as trypsin in adult F. paulensis. The digestive proteinase pattern of adult Farfantepenaeus californiensis, F. paulensis, L. schmitti and Litopenaeus vannamei in SDS-PAGE showed clear differences among these species, which may be evidence of a species-specific pattern of protein digestion. In vitro evaluation of digestibility of aquafeeds can be achieved by the pH-stat method, which can help in the choice for alternative protein sources. Moreover, the quality of postharvest shrimp may also be affected by increased digestive proteinase activity that seems to be stimulated by low nutritional quality feeds.