Effects of storage on product quality of bivalves (oysters, scallops, and clams)

The purpose of this thesis is to investigate the effects of the different storage conditions concerning quality of oysters Ostrea edulis, scallops Pecten maximus and clams Arctica islandica. Quality of bivalves is a very broad concept dependent of several factors such as the preferences of the consumer, the conditions which the animals have grown, harvest methods as well as the level of stress post-harvest. The organoleptic characteristics, such as the appearance and smell, are very important in the perception of quality by the consumer, and these factors might be the most decisive for the acceptance of the food product. The bivalves which are harvested during different seasons might have different quality. Seasonality can have influence on the sensorial characteristics since there are biochemical changes in the body of these molluscs throughout the year, due to the feed and the reproduction stages. Moreover, the bivalves which are subject to high levels of stress conditions will be of lower quality. The stress, whether due to environmental factors (food availability, salinity, temperature and water quality) or due to the harvest and post-harvest (fishing methods, storage conditions), will influence survival during storage and in therefore, influence the quality of the final product. In this study, wild bivalves were stored alive in polypropylene boxes at different temperatures (3, 6, and 9 ºC) during different days (3, 6, 9 and 12 days) and the quality was verified through a sensory evaluation, weight assessment and survival. The evaluation of quality was carried out with two different sizes of oysters, two different sizes of scallops and one size of clams. In addition, was verified the relationship between the quality, and the season variability. The results showed that the variability of the oysters’ quality between seasons, temperature and time of storage were not a significant (p > 0.05). The survival rate was high during the storage (6 deaths in 168 oysters) and the influence of the storage conditions was not significant. Regarding to scallops, it was concluded that with the increase of both temperature and time of storage, quality decreases. Scallops can be stored until 7 days at 3 ºC without loose quality and only until 3 days at 6 and 9 ºC. Once, after the day 3 at 6 and 9 ºC, all scallops died can be concluded that the survival of the scallops and the storage conditions were related. Moreover, the season which the scallops were harvested was significant in the final quality of the product, being August the best season for harvesting. Regarding the clams, the conditions of the storage described on this paper as well as the season of harvest were not significant. The survival of clams was high (5 deaths in 72 individuals) and so, the relationship with storage conditions was not significant (p > 0.05). The results of the sensory quality evaluation for oysters and clams showed a good quality for these bivalves subject to different temperatures and time of storage.

Master's Thesis in Biology

MAMN-BIO

BIO399