Benjamin K. Simpson

Spoilage and shelf-life extension of fresh fish and shellfish.

Fresh fish and shellfish are highly perishable products due to their biological composition. Under normal refrigerated storage conditions, the shelf life of these products is limited by enzymatic and microbiological spoilage. However, with increasing consumer demands for fresh products with extended shelf life and increasing energy costs associated with freezing and frozen storage, the fish-processing industry is actively seeking alternative methods of shelf life preservation and marketability of fresh, refrigerated fish and at the same time economizing on energy costs. Additional methods that could fulfill these objectives include chemical decontamination, low-dose irradiation, ultra-high pressure, and modified atmosphere packaging (MAP). This review focuses on the biochemical and microbiological composition of fresh fish/shellfish, the spoilage patterns in these products, factors influencing spoilage, and the combination treatments that can be used in conjunction with refrigeration to extend the shelf life and keeping quality of fresh fish/shellfish. The safety concerns of minimally processed/MAP fish, specifically with respect to the growth of Clostridium botulinum type E, is also addressed.

Aflatoxins in food: Occurrence, biosynthesis, effects on organisms, detection, and methods of control

Aflatoxins are secondary metabolites produced by species of Aspergilli, specifically Aspergillus flavus and Aspergillus parasiticus. These molds are ubiquitous in nature and grow on a variety of substrates, thereby producing aflatoxins. Aflatoxins are of great concern due to their biochemical and biological effects on living organisms. In this article, the occurrence of aflatoxins, their biosynthesis, factors influencing their production, their effects on living organisms, and methods of detection and control in food are reviewed. Future areas of research involving mathematical modeling of factors influencing aflatoxin production and alternative methods of control, such as modified atmosphere packaging, are also discussed.

Removal of Selected Metal Ions from Aqueous Solutions Using Chitosan Flakes

Commercially available chitosans potential in the adsorption of heavy metals like zinc, copper, cadmium, and lead from aqueous solutions under variable physicochemical conditions was investigated. The results obtained from equilibrium and kinetic studies showed that there was significant uptake of these metal ions by chitosan and that chitosan flakes had a maximum sorption capacity for copper ions. The order of metal ion adsorption by chitosan decreased from Cu2+ to Zn2+ as follows: copper lead cadmium zinc. There was a considerable increase in sorption capacity with an increase in chitosan amount; however, this parallelism diminished when the chitosan mass exceeded 0.24 g in 25 mL of metal solution. The sorption of metal ions from various salt solutions by chitosan flakes was not improved by agitation. The heavy metal uptake by chitosan was found to be pH-dependent, with a maximum at pH 6.0 and 7.0. Sorption equilibrium studies were conducted with a constant sorbent weight and varying initial concentration of metal ions. The experimental data of adsorption from solutions containing metal ions were found to correlate well with the Langmuir isotherm equation.

Application of high hydrostatic pressure to control enzyme related fresh seafood texture deterioration

Abstract Enzyme extracts from two fish species, bluefish and sheephead, were subjected to hydrostatic pressure treatments ranging between 1000–3000 atm for various durations and the residual activities of cathepsin C, collagenase, chymotrypsin- and trypsin-like enzymes compared with those of their bovine counterparts. The fish enzymes were generally more susceptible to hydrostatic pressure inactivation than their mammalian counterparts. Fresh fish muscle tissues were also subjected to similar pressures and the color and textural parameters determined. The color generally became lighter presenting a cooked appearance to the fresh fish flesh with increasing pressure as well as holding time. There was general toughening/ hardening of the tissue when 1000 atm of pressure was applied. The upper limit for maintaining or enhancing tissue hardness was the application of 2000 atm for 10 min. Beyond this point, the tissue generally becomes softer with pressure and holding time.

Developments in food packaging technology. Part II. Storage aspects

Abstract The shelf life of many perishable foods, such as meat, eggs, fish, poultry, fruits, vegetables and baked products, is limited in the presence of atmospheric oxygen due to three important factors: the chemical effect of atmospheric oxygen, the growth of aerobic spollage microorganisms and attack by insect pests. Each of these factors, alone or in conjuction with one another, results in changes in colour, flavour and odour, and leads to an overall deterioration in food quality. In Part I of this two-part series, recent developments in packaging technology, with reference to selected processing methods, such as aseptic packaging and packaging innovations related to microwavable foods, were discussed. Part II reviews modified atmosphere packaging (MAP) and sous-vide (vacuum cooking) processing. Both of these preservation techniques are used extensively for the extension of food shelf life in Europe, and are now gaining acceptance as preservation techniques in the USA and Canada.

Use of proteolytic enzymes to facilitate the recovery of chitin from shrimp wastes

Abstract Two proteolytic enzymes, chymotrypsin and papain, were used to hydrolyze proteins associated with demineralized shrimp waste to recover chitin. The conditions used were optimized using response surface methodology (RSM). The factors studied were temperature (3 levels), pH (3 levels) and enzyme to waste ratio (E/W ratio)(5 levels). Of these, pH was the most important factor in the models obtained. Optimum conditions for deproteinization by chymotrypsin were determined to be around 40°C, pH 8.0 and E/W ratio of 7.1000 (w:w). With papain, a temperature of around 38°C, pH of 8.7 and E/W ratio of 10:1000 (w:w) gave the optimum response. At these conditions, the yield of protein was maximum, and ranged from 22–48% depending on the starting material. The residual protein levels in the waste after deproteinization with the enzymes were very low, i.e., 1.3 and 2.8% for chymotrypsin and papain‐treated samples, respectively.

Effect of freezing conditions and storage on ice crystal and drip volume in turbot (Scophthalmus maximus): Evaluation of pressure shift freezing vs. air-blast freezing

Abstract Turbot fillets were frozen either by pressure shift freezing (PSF, 140 MPa, −14°C) or by air-blast freezing (ABF), and then stored at −20°C for 75 days. Smaller and more regular intracellular ice crystals were observed in fillets frozen by PSF compared with air-blast frozen ones. Ice crystals area in PSF samples was approximately 10 times smaller than that of ABF samples, on average. The PSF process reduced thawing drip compared with air-blast freezing. Conversely to this classical freezing process, the storage time did not adversely influence the thawing drip of PSF samples. In addition, PSF appeared to reduce cooking drip after 45 days of storage at −20°C. Differential scanning calorimetry analysis showed a significant reduction of the total enthalpy of denaturation for the pressure shift frozen samples compared to fresh and conventional frozen samples. Besides, a new melting transition appeared on the thermogram of PSF samples at approximately +40°C.

Application of enzymes in food processing

Enzymes offer potential for many exciting applications for the improvement of foods. There is still, however, a long way to go in realizing this potential. Economic factors such as achievement of optimum yields and efficient recovery of desired protein are the main deterrents in the use of enzymes. Changing values in society with respect to recombinant DNA and protein engineering technologies and the growing need to explore all alternative food sources may in time make enzyme applications more attractive to the food industry. Research is continuing on the commercially viable enzymes in use today to improve various properties such as thermostabilities, specificities, and catalytic efficiencies. New and unique enzymes continue to be developed for use in enzymatic reactions to produce food ingredients by hydrolysis, synthesis, or biocatalysis. An aggressive approach is needed to open new opportunities for enzyme applications that can benefit the food industry.

Utilization of chitosan for preservation of raw shrimp (Pandalus borealis)

Abstract Whole and headless shrimp (Pandalus borealis) were dipped in various concentrations of chitosan solution and stored for 20 days at 4–7°C. The effects of chitosan on microbial proliferation, total volatile bases, nucleotide breakdown, and blackspot formation were monitored over this period. Chitosan showed strong antimicrobial properties inhibiting several microorganisms at concentrations ranging between 0.0075 ‐ 0.01%. The Pseudomonads, however, were very resistant to chitosan requiring much higher concentrations (0.1%) for inactivation. Chitosan reduced the levels of total volatile bases but had no effect on nucleotide breakdown. On the incidence of melanosis, there were no significant differences (p > 0.05) between samples treated with chitosan and the non‐treated samples although blackspot formation was more extensive in whole than headless shrimp. Furthermore, treatment of shrimp with 2% chitosan showed consistently lower incidence of melanosis during storage. The results suggest that chitosa...

Lipases from Mammals and Fishes

Lipases are a broad family of enzymes that catalyze the hydrolysis of ester bonds in substrates such as triglycerides, phospholipids, cholesteryl esters, and vitamin esters. Lipases are receiving increasing interest due to their effects on the quality of food products (e.g., the quality of post-harvest seafoods), and their actual and potential applications in modified foods and industrial processes. Lipases that catalyze specific reactions and that are active at particular conditions of pH and temperature to suit the requirements of industrial processes are of particular interest. This review focuses on lipases that display predominantly triacylglycerol hydrolase activity. Section 1 presents an overview of lipases from terrestrial organisms and the lipase gene family members. Due to their unique physiology, diet, and habitat, fish lipases may demonstrate novel activities that have potential applications for bioindustrial catalysis. Section 2 discusses lipases from fish and compares them with lipases from mammals and birds. Purification strategies and properties of the isolated enzymes are reviewed in detail.