Seasonal variations in chemical, physical, textural, and microstructural properties of adductor muscles of Pacific lions-paw scallop ( Nodipecten subnodosus)

Abstract

This study analyzes the relationship between the physiological state of the Pacific lions-paw scallop Nodipecten subnodosus and the quality of the meat, in relation to two environmental variables (temperature and chlorophyll a concentration). Muscle and gonadosomatic indices, gonadal stage, and glycogen were determined in scallops of similar size (66.3 ± 6.9 mm) as indicators of their physiological state. The scallops were harvested once every season from a shellfish farm located at Laguna Manuela, Mexico. Quality of adductor muscles was determined by means of pH, water-holding capacity, color parameters, proximate composition, free amino acid content, texture, collagen, and microstructure. As a reference, temperature was recorded every half hour and chlorophyll a every fifteen days from January to November 2003. Results indicate that temperature and chlorophyll a concentrations peaked in September (summer), matching the highest muscle and gonadosomatic indices and glycogen content. In summer, carbohydrate concentration and weight of muscles were highest and color was whiter and brighter. However pH was significantly lower making water-holding capacity drop to the lowest level recorded, increasing the probability of water loss during handling, processing, and storage. Amino acid content was also affected by season. Concentration of several amino acids that give sweet flavor to meat (glycine, arginine, taurine, and alanine) dropped. Humidity, protein, and lipid concentrations also decreased, making the muscles tenderer, as confirmed by texture parameters of cut, hardness, elasticity, chewiness, gumminess, and adhesiveness. Changes in texture were explained by a decrease in collagen, which is an important component of connective tissue, and a lower density of muscle fibers per surface area. With these results, the definition of the optimum harvest season is controversial. Despite a higher weight per muscle in summer, muscles show the lowest quality, considering most of the parameters studied.