UBC Theses and Dissertations
Headspace gas chromatography for quality assessment of canned Pacific salmon Girard, Benoit
The method currently established to assess the quality of canned Pacific salmon relies on sensory evaluation. Among the sensory attributes of importance, odour plays a determining role in grade assignment. It would therefore be useful to obtain information about the volatile components which can be indicative of various quality criteria. This study was primarily undertaken: (1) to analyze the headspace volatiles of canned salmon with a rapid method, (2) to apply multivariate statistics on the headspace volatile data for classifying canned salmon in terms of species, sexual maturity, and degree of decomposition, and (3) to investigate the perceived odour of canned salmon volatiles separated by dynamic headspace gas chromatographic methods. Sample weight, incubation temperature and time were studied to develop a static headspace sampling method for volatiles in canned salmon. A random-centroid optimization program (RCO) simultaneously searched for the optimal levels of other factors, namely, initial oven temperature, column headpressure, and total flowrate. RCO was found to be an effective optimization program which allowed the performance of several treatment runs at a time. Optimal conditions of operation permitted the detection of 80 volatile compounds, 34 of which were identified including aldehydes, alkanes, aromatic compounds, sulfur-containing compounds, alkenes, ketones, several other compounds plus an alcohol and an acid. Forty-four selected headspace volatiles from cans of 4 species of Pacific salmon (chum, coho, pink, sockeye), chum salmon at 3 stages of sexual maturity, and pink salmon of 3 quality grades were quantitatively determined using the static headspace gas chromatographic (SHGC) method, and analyzed by multivariate statistical methods. Principal component analysis (PCA) and common factor analysis (CFA) facilitated the interpretation and further handling of the collected gas chromatographic data by transforming them into ten or fewer important dimensional factors. Discriminant analyses (DA) were applied to the PCA scores for group classification. In light of non-compliance of statistical assumptions by the newly generated variables, error rates of linear, quadratic, and non-parametric functions computed by the resubstitution and cross-validation methods were compared. The non-parametric (NPAR) Epanechnikov kernel method maintained a 90% rate or higher of effectiveness at segregating canned salmon of different species, stages of sexual maturity, and quality levels. NPAR-DA also provided a high degree of discrimination at the beginning of refrigerated decomposition where the detection of spoilage by sensory grading is uncertain. Ethanol and 3-methyl-1-butanol contributed significantly to classification of quality grade of canned pink salmon. Dynamic headspace concentration by Tenax trap sampling/gas chromatography/mass spectrometry (TTS/GC/MS) and cryofocussing concentration sampling/gas chromatography/odour evaluation (CCS/GC/OE) were other means used to analyze volatile components of canned pink salmon, grade A and reject, and canned late-run chum salmon. A total of 130 compounds were identified; hydrocarbons and ketones were found in large numbers followed by sulfur-containing compounds, nitrogen-containing compounds, alcohols, aldehydes, and acids. The headspace profile of all analyzed samples possessed several odour attributes which were associated with the chemical structures identified. No single compound was responsible for the characteristic aromas of canned pink salmon, grade A or reject. 2-Methyl-butanal and two lower boiling point unknowns had a hay or straw-like, cooked-malt odour typical of canned chum salmon of spawning maturity.
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