Date of Award

5-2003

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Food Science and Human Nutrition

Advisor

Denise Skonberg

Second Committee Member

Alfred A. Bushway

Third Committee Member

Mary Ellen Camire

Abstract

Millions of pounds of crab and shrimp shell waste are created every year by the seafood industry. This waste is very resistant to biodegradation and disposal is problematic. Crustacean shells are composed mainly of chitin that can be converted to chitosan by deacetylation. Many current shelf life extension and pathogen inhibition methods employ the use of various chemical preservatives. Chitosan, an abundant natural polysaccharide, possesses antimicrobial as well as functional properties that may be useful in improving quality of stored foods. These properties may be influenced by a number of factors that must be studied before determining the most useful food applications of chitosan. The objectives of this research were to: 1) study the efficacy of powdered chitosan and chitosan dips in enhancing the refrigerated shelf life of minced salmon trim and salmon fillets; 2) determine the feasibility of degrading chitosan with commercially available enzymes, alpha amylase and bromelain; and 3) study the effects of native and enzymatically degraded (with alpha amylase) chitosans in vitro, in two different media, against Pseudomonas aemginosa and Listeria innocua. The first study examined the effects of 1% high (HMW) and low molecular weight (LMW) chitosan dips (prepared in 1% acetic acid) applied to salmon fillets as well as powdered HMW and LMW chitosan mixed into salmon trim. The effects were measured over the course of two weeks of refrigerated storage and the analyses included: total aerobic plate counts (APC), total volatile base nitrogen (TVBN), and pH. The results of this study indicated that HMW chitosan dips could effectively reduce aerobic plate counts and reduce WBN values of salmon fillets and thereby extend refrigerated shelf life. Mixing powdered native chitosan in salmon trim resulted in no significant differences among treatments. The second study examined the abilrty of two common enzymes, alpha amylase and bromelain, to degrade chitosan solutions to confer water solubility to the chitosan at neutral pH. Results of this study indicated that bromelain was ineffective, however alpha amylase was able to degrade chitosan solutions as was evidenced by reduced solution viscosity and increased water solubility at neutral pH. The third study examined the antimicrobial effects of different concentrations of alpha amylase degraded (for 10 minutes, I hour and 24 hours) and native chitosans against Listerie innocua and Pseudomonas aemginosa in nutrient (NB) and trypticase soy broth (TSB) over 4 days at 4°C. Chitosan treatments effectively reduced Listeria counts in TSB by at least one log, but only significantly so on day three. The 24 hour degraded chitosan and lower percentage chitosan treatments were the least effective. No significant reductions in Pseudomonas counts were observed in TSB for any treatment. In NB all the chitosan treatments had significantly (~~0.05) lower (up to 3.4 logs) Pseudomonas counts than both controls on all four days. Log reductions increased with increasing chitosan percent. Ten minute degraded chitosan had slightly greater log reductions compared to other treatments. The results of this experiment indicated that the antimicrobial effectiveness of chitosan depended on the nutrient matrix, chitosan concentration, degradation time, and bacteria type- The results of this research indicate that chitosan must be solubilized to act as an antimicrobial agent in salmon. Chitosan can be degraded successfully by alpha amylase, producing a water soluble chitosan that may have a use in a product such as minced salmon trim. In vitro antimicrobial action of the chitosan decreased with increasing degree of degradation and depended greatly on the type of media used, indicating that many factors may influence the effectiveness of chitosan in a real food system. Future research should be done to determine if the enzymatically produced water soluble chitosan can act as an antimicrobial agent when incorporated into salmon trim or when used as a dip on salmon fillets.

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