Abstract
While attempting to develop a soft, seafood-based product as a potential food item for senior citizens, we evaluated the effects of different softening methods on the hardness and quality of thawed muscular mantle tissue of the neritic squid (Uroteuthis edulis) versus controls. Comparisons were made among injection with proteolytic enzymes (papain, bromelain); soaking in these enzymes or in alkali solutions (NaHCO3, NaOH); various soaking regimes combined with either orbital shaking under vacuum, ultrasonic processing, or ultrasonic cleaning; or hot-air drying and rehydration. Elderly panelists’ sensory impressions of thawed and heat-sterilized squid mantle subjected to these treatments were recorded, together with the total volatile basic nitrogen (TVBN), pH, color, protein breakdown profile (SDS-PAGE), and histological characteristics of thawed squid mantle subjected to the same treatments but not heat-sterilized. TVBN measurements showed that squid mantle remained in a close-to-fresh state under all treatments except for hot-air drying. The pH and hardness decreased and the muscles turned white when soaked in either enzymes or alkali. Orbital shaking under vacuum while soaking in 0.3% papain for 12 h produced the softest product, the next softest being obtained by injection with 0.3% papain. After orbital shaking under vacuum in 1.0% papain, protein degradation was confirmed by SDS-PAGE, and broken muscle fibers were evident in histological sections. Sensory evaluation panelists with unimpeded chewing ability rated mushy, papain-treated squid mantle poorly. Soaking in 2% NaHCO3 in an ultrasonic processor, following by washing out of the alkali, proved to be a better tenderizing method than either enzyme treatment or hot-air drying for neritic squid mantle intended for consumption by senior citizens.
Highlights
Neritic squid (Uroteuthis edulis, formerly called Loligo edulis; often called squid) is the major species in the squid fishery of Keelung, Taiwan, with an estimated take of 3780 metric tons worth NTD 530 million in 2013 [1]
Soaking in an alkali solution resulted in softening of test samples of squid mantle, with the effect being greater in 2% NaOH than in 2% NaHCO3 (p < 0.05) (Table 1)
The pH of squid mantle soaked in 2% NaOH (9.93) was significantly higher than that of samples soaked in 2% NaHCO3 (9.16) or a control sample (7.59)
Summary
Neritic squid (Uroteuthis edulis, formerly called Loligo edulis; often called squid) is the major species in the squid fishery of Keelung, Taiwan, with an estimated take of 3780 metric tons worth NTD 530 million in 2013 [1]. Neritic squid contains high amounts of protein, taurine, omega-3 polyunsaturated fatty acids, iodine, selenium, vitamins B12 and D, essential amino acids, and phospholipids [2]. Squid mantle contains a high amount of insoluble myostromin [3], making its meat tough and hard to chew compared to that of fish. Squid mantle muscle fibers, arranged both radially and circularly, are supported by connective tissue that is oriented in radial, circular, and longitudinal directions [4]. This has made it difficult to adapt squid mantle into a softer processed food for older people.
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