Rosalee S. Rasmussen

Marine Biotechnology for Production of Food Ingredients

The marine world represents a largely untapped reservoir of bioactive ingredients that can be applied to numerous aspects of food processing, storage, and fortification. Due to the wide range of environments they survive in, marine organisms have developed unique properties and bioactive compounds that, in some cases, are unparalleled by their terrestrial counterparts. Enzymes extracted from fish and marine microorganisms can provide numerous advantages over traditional enzymes used in food processing due to their ability to function at extremes of temperature and pH. Fish proteins such as collagens and their gelatin derivatives operate at relatively low temperatures and can be used in heat-sensitive processes such as gelling and clarifying. Polysaccharides derived from algae, including algins, carrageenans, and agar, are widely used for their ability to form gels and act as thickeners and stabilizers in a variety of foods. Besides applications in food processing, a number of marine-derived compounds, such as omega-3 polyunsaturated fatty acids and photosynthetic pigments, are important to the nutraceutical industry. These bioactive ingredients provide a myriad of health benefits, including reduction of coronary heart disease, anticarcinogenic and anti-inflammatory activity. Despite the vast possibilities for the use of marine organisms in the food industry, tools of biotechnology are required for successful cultivation and isolation of these unique bioactive compounds. In this chapter, recent developments and upcoming areas of research that utilize advances in biotechnology in the production of food ingredients from marine sources are introduced and discussed.

A Review of Mercury in Seafood

ABSTRACT Mercury is a toxic heavy metal released into the environment from both natural and anthropogenic sources. It is of great interest to consumers as to whether it can cause neurological effects at low dose levels. The effects of organic mercury exposure at high levels have been demonstrated in several large-scale poisonings, particularly those in Japan and Iraq in the 1950s, ′60s and ′70s. These epidemics showed that organic mercury, in sufficient concentrations, is a potent neurotoxin that is especially harmful to the developing nervous system. Since the most common form of human exposure to organic mercury is through fish consumption, several epidemiological studies have examined the relationship between maternal fish intake and health effects in humans, especially the fetus. Levels of mercury in fish vary depending on factors such as: trophic level in the food chain, size, and habitat location. For this reason, it is important to gather information on mercury levels in different types of fish in various parts of the world. Results of recent studies have caused the Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) to issue new advisories on the fish consumption for pregnant women and young children. However, there is concern that other individuals will significantly reduce their fish consumption also, thereby decreasing the potential health benefits of seafood. This review is meant to promote understanding of current issues regarding mercury in seafood and provides a compilation of up to date information on the following topics: background information on mercury; large scale mercury poisonings; epidemiology studies and risk assessment; and studies on mercury in tuna in different geographical locations.

Mercury Content in Pacific Troll-Caught Albacore Tuna (Thunnus alalunga)

Abstract Ninety-one albacore tuna (Thunnus alalunga) captured during the 2003 commercial fishing season were tested for total mercury content in muscle tissue. The fish were harvested between 32.72°N (off Southern California) and 48.30°N (off the northern tip of Washington) between July and November. Fish weighed from 3.14 to 11.62 kg and were 50.8-86.4 cm long. Total mercury content in the albacore muscle tissue ranged from 0.027 ppm (μg/g) to 0.26 ppm. The average total mercury content was 0.14 ± 0.05 ppm, which is below the U.S. Food and Drug Administration action level and Canadian standards (1.0 ppm methylmercury and 0.50 ppm total mercury, respectively). Total mercury concentrations showed positive correlations with length and weight of albacore (R2= 0.40 and 0.38, respectively), but there was no correlation with date of capture or lipid content. Results indicate that Pacific troll-caught albacore have low levels of total mercury in the edible flesh and are well within international safety standards for mercury levels in fish.

Application of a PCR-RFLP Method to Identify Salmon Species in U.S. Commercial Products

A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method for salmon species identification was optimized for use with U.S. commercial products. Reference specimens of six salmonid species were collected and morphologically verified. A 463- to 464-bp fragment of the mitochondrial tRNAGlu/cytochrome b gene was PCR-amplified, digested with two restriction enzymes (Sau3AI and NlaIII), and analyzed with agarose gel electrophoresis. All six species were successfully differentiated with this method and the restriction digest was shortened to 1 h rather than overnight. A decision-making flowchart was developed based on these results that allows for species diagnosis within two–three steps. After the method was optimized, it was tested with a variety of commercial salmon products (n = 29), including canned, smoked, jerky, and fresh fillet samples. Salmon species identification was successful for all 14 smoked and fresh/frozen fillet products, with the possibility of same-day species diagnosis. Species identification was also achieved for two out of three jerky products, but required overnight lysis. The remainder of the samples could not be diagnosed—including canned salmon, pouch-sterilized salmon, and canned paté. Overall, this method showed high potential for use in same-day species authentication with lightly processed seafood, but heavily processed products will require alternate methods.

EFFECT OF AGE AND TISSUE WEIGHT ON THE CADMIUM CONCENTRATION IN PACIFIC OYSTERS (CRASSOSTREA GIGAS)

Abstract This study investigated the influence of age and tissue weight on cadmium (Cd) levels in Pacific oysters (Crassostrea gigas). Oysters from 4 different age groups (1, 2, 3, and 4 y) were collected at an oyster farm in Willapa Bay, Washington. To examine the effects of age, 60 oysters from each group were sorted into 3 composites of 20, and Cd analysis was carried out on all composite samples. To study the effects of tissue weights, 25 oysters from each of the 4 age groups were collected and analyzed individually for Cd. All oyster Cd concentrations were below the 3.7 ppm (μg/g) wet wt Food and Drug Administration (FDA) level of concern and the 2 ppm wet wt Hong Kong limit. There was a moderate correlation between Cd concentration and age (R2 = 0.60). The 1-y-old oysters had significantly lower Cd concentrations than the 2–4-y-old oysters. Tissue weight also influenced Cd concentration (R2 = 0.31). The effect of tissue weight was found to vary with age, with a stronger correlation to Cd levels in the 1- and 2-y-olds and a weaker correlation among the 3- and 4-y-olds. The results indicate that oysters accumulate the majority of their Cd during the first two years of their lives, after which point they become saturated and show only incremental additions of Cd in later years.

Effect of Seasonality, Location, and Size on Lipid Content in North Pacific Troll-Caught Albacore Tuna (Thunnus alalunga)

ABSTRACT Two hundred and thirty-nine albacore tuna (Thunnus alalunga) were troll-caught in the mid-Pacific Ocean and off the US Pacific Coast from June to November 2003. Catch location, harvest date, and sea surface temperature were recorded for individual fish, and lipid and moisture content in the white muscle were determined. The average weight of the alba-core was 6.07 kg and lipid content was highly variable (0.67–18.74%). There was an inverse correlation between the lipid and moisture content of albacore (R2 = 0.93), and percent lipid increased slightly in fish caught later on in the season (R2 = 0.24). Geographical Information Systems (GIS) software was used to determine correlations between lipid content and geographic location. Lipid content varied considerably among tuna caught at similar latitudes; however, most fish caught below 40°N had a lipid content of less than 10%, while the fish with the highest lipid content (13–19% lipid) were all harvested above 40°N.

The Effects of Processing Methods and Storage on Cadmium Levels in Pacific Oysters (Crassostrea gigas)

ABSTRACT The effects of processing and storage on cadmium (Cd) levels in Pacific oysters (Crassostrea gigas) were examined. The oysters were 2.75 yrs old and were analyzed for Cd at various points in the processing line including: shucked (S), shucked and drained (SD), and shucked, drained, washed and jar-packed (S-WJ). The effects of high pressure processing (HPP) followed by washing and jar-packing were also examined. Jar-packed oysters from groups S-WJ and HPP were held under refrigerated storage and were analyzed at 0, 5 and 10 days. Some processing methods had significant effects on the Cd levels in oysters. Draining nectar from the oysters resulted in significant increases in Cd concentrations, followed by significant decreases as a result of washing and jar-packing. HPP-treated oysters that were washed and jar-packed showed further decreases in Cd. Ten days of jar-packed storage resulted in a gradual decrease in wet weight Cd concentration for both the HPP (from 1.1 to 0.8 mg/kg) and the S-WJ groups (from 1.4 to 0.9 mg/kg). Total tissue Cd levels decreased significantly during storage of oysters in Group S-WJ, while tissue weights increased significantly. These findings suggest that changes in Cd concentration may have been due to a combination of a release of Cd by the oyster tissue and a dilution of the available Cd due to water uptake.

Fatty Acid Composition of U.S. West Coast Albacore Tuna (Thunnus alalunga) and the Effects of Canning and Short-Term Storage

ABSTRACT Changes in the fatty acid composition of 13 bled and blast-frozen U.S. West Coast albacore tuna (Thunnus alalunga) were determined following custom-canning and 5 weeks of canned storage. In accordance with typical custom-canning procedures, no additional packing materials were used, and the product did not undergo a precooking step. Raw albacore tuna was found to be rich in n-3 polyunsaturated fatty acids (PUFAs), with an average of 9.1% (% wt of total fatty acids) EPA and 33.8% DHA. Canning and short-term storage did not cause major fluctuations in the fatty acid profiles of the albacore tuna, with no significant changes in the total fractions of saturated fatty acids (30–31%), monounsaturated fatty acids (19%), PUFAs (50%), or n-3 PUFAs (46–47%). On a tissue weight basis, U.S. West Coast albacore tuna was found to contain high levels of total n-3 PUFAs, with 3.3 g/100 g tissue in raw tuna and 4.0–4.1 g/100 g tissue in products that were canned and stored for 5 weeks.