Tài liệu Formation of volatile acids during fermentation of fish sauce

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5 FORMATION OF VOLATILE ACIDS DURING FERMENTATION OF FISH SAUCE Norlita G. Sanceda,1 Emiko Suzuki,2 and Tadao Kurata l IInstitute of Environmental Science for Human Life Ochanomizu University, Tokyo, Japan 2Department of Human Biological Studies Ochanomizu University, Tokyo, Japan The formation of volatile acids in fish sauce was investigated. When fish was allowed to spoil prior to salting, very high concentrations of volatile acids were produced. Addition of salt to spoiled fish suppressed the formation of volatile acids but did not eliminate those already formed. It was clarified that volatile acids were formed by atmospheric oxidation of lipid and normal acids were derived from long chain fatty acids. The volatile acids in the aerobically fermented sauce were significantly higher than in the anaerobically fermented sauce which might also suggest atmospheric oxidation of lipids. Increasing the amount of amino acids in the fish mixtures did not provide any clear information about their role in the formation of volatile acids during the fermentation process. INTRODUCTION Fish sauce is a clear brown liquid, hydrolysis product of salted fish and possesses a characteristic odor. It is one of the most popular fermented fish products in Southeast Asia and is known by various names according to the country of origin (for example, Patis in the Philippines; Nampla in Thailand; Ngampi-pya-ye in Burma or presently Myanmar; Shottsuru in Japan; Ketjap-ikan in Indonesia; or Nuocmam in Vietnam). It is generally used as a condiment, but it is also an important source of protein in the diets of some social classes and in specific areas in the region. Lafont (1955) reported that fish sauces should not be considered as condiments only. Those with I % nitrogen or more could be considered as rather better than condiments. Fish sauces contain 20 g IL of nitrogen, of which 16 giL are in the form of amino acids. Fish sauce is prepared by salting fish at a ratio of 2: I or 3: I depending on the quality of fish used and the salt used in its manufacture. Fish that exhibit some form of deterioration require a ratio of 2: 1 while a ratio of 3: 1 suffices if the fish is relatively fresh. The fish-salt mixture is then placed in clay jars, wooden or concrete vats. To facilitate extracFlavor Chemistry of Ethnic Foods. edited by Shahidi and Ho Kluwer Academic / Plenum Publishers. New York. 1999. 41 42 N. G. Sanceda et al. tion and increase the yield, weights, usually hard stones, are placed on top of the mixture. The fish sauce manufacturing process is complete when the characteristic flavor, aroma and color develop. The sauce is extracted, filtered, pasteurized and bottled. The first extract may be considered as extra special and sold as such. STANDARD IDENTITY OF FISH SAUCES IN THE PHILIPPINES The standard set by Food and Drug Administration (FDA), 1980 for Philippine fish sauce is as follows: a. Specific gravity, 1.21-1.22 b. Total solids, Not less than 32% c. Alkalinity of the water soluble ash of one gram of original sample. Not less than 1 and not more than 2 mL ofO.lN acid d. Protein: 1. Extra special patis, not less than 12% 2. Special patis, not less than 10% 3. Regular patis, Not less than 6% 4. Patis below standard or patis flavor, below 6% but not lower than 3%. There are a number of reports on the kinds of volatile compounds in fish sauces. Earlier studies revealed that low-molecular-weight volatile compounds such as methyl ketone (van Veen, 1953), organic acids (Nguyen and Vialard-Goudou, 1953; Truong, 1963; Yanagihara et al., 1963) and carbonyl compounds (Yurkowski, 1965 a,b) have been reported to contribute to the flavor of fermented fish products. Particularly, organic acids were shown to be associated with the aroma of fish sauce (Vialard-Goudou, 1941 and 1942; Nguyen and Vialard-Goudou, 1953; Truong, 1963). Volatile acids which contributed to the aroma of fish sauce would have been produced by bacterial activity (Saisithi et al., 1966). However, there was no detailed report on the extent of their role on the aroma quality. Martin and Sulit (1953) reported a characteristic cheese-like odor and flavor in fish paste. Dougan and Howard (1975) reported that the aroma of fish sauce consisted of three notes; "cheesy note" produced by low molecular weight fatty acids, "ammoniacal note" by ammonia and amines" and meaty note", but the meaty odor was more complicated thus was not analyzed. Sanceda et al. (1986) reported some volatile compounds in several kinds of fish sauces as summarized in Table 1 and graphically presented in Figures 1-3. Although quantitative analysis was not done in this study, the gas chromatograms suggested that volatile acids were the most abundant among the compounds identified. This data is supported by the results presented in Table 2. The sauce has a characteristic aroma which often serves as a gauge to measure the quality of fish sauce, since the very salty taste tends to overpower the other flavor constituents. A number of reports revealed that volatile acids were the most abundant group of volatile compounds in fish sauce. Formic, acetic, propionic, and n-butyric acids were identified by Truong Van-Chom (1963) and Saisithi et al. (1966) obtained similar results except that they identified iso-butyric acid instead of n-butyric acid. Patis, nuocmam, nampla and shottsuru contained volatile acids with C2 to C 10, both straight and branched-chain. Acetic, propionic, iso-and n-butyric, and iso-valeric acids were identified in the acidic fraction of the steam distillate of patis (Sanceda et aI., 1983, 1984) and in other samples by Dougan and Howard (1975) and Beddows et al. (1979). Propionic and n-Butyric acids were predominant in patis (Sanceda et al., 1984), both are believed to have unpleasant odor but the Formation of Volatile Acids during Fermentation ofFish Sauce 43 Table 1. Concentrations of volatile acids in fresh and spoiled fish (%)" Incubation period, days Acids 0 Fresh fish Acetic Propionic Isobutyric Butyric Isovaleric Valerie 0.10 0.07 0.07 0.09 0.14 O.OS ± ± ± ± ± ± 3 0.12 0.08 0.07 0.14 0.14 O.OS 0.02 0.02 0.01 0.03 0.03 0.01 4 ± 0.01 ± 0.03 ± O.oJ ± 0.02 ±0.02 ± 0.01 0.13 0.08 0.07 0.18 O.lS O.OS ± ± ± ± ± ± 0.01 0.02 0.03 0.04 0.02 0.01 4 with salt without salt 0.90± 0.02b 0.87 ± 0.03 b 0.70 ± 0.02b 2.S8 ± O.OSb 0.61 ± 0.01 b 0.73±0.0Ib 1.78 ± 0.0 I b.c 1.02 ± 0.01 b.c 0.97 ± 0.02 b.c 3.79 ± O.OSb.c 0.91 ± 0.03 b.c 1.03 ± O.03 b.c 3 Spoiled fish Acetic Propionic Isobutyric Butyric Isovaleric Valerie O.SI 0.43 0.6S 2.00 O.SO 0.68 ± O.Olb ± 0.03 b ± 0.03 b ± O.OSb ± 0.02b ± O.Olb 'Values are means of three replicates. Fresh fish were stored at O°C for one day before purchase and left to spoil at room temperature. Fresh fish and spoiled fish: salt ratio was 3: 1. Values of acids in the 3 and 4 days incubated fresh fish are not significantly different from the control (0 day). bValues of the acids in the spoiled fish are significantly different at p<0.05 with their respective acids in the fresh fish in the corresponding incubation period. 'Values of the acids in the spoiled fish without salt incubated for 4 days are significantly different at p<0.05 from those incubated with salt. 25 30 34 36 1 53 BHT 28 Figure 1. Gas chromatogram of the whole volatile distillate ofShottsuru. 44 N. G. Sanceda et al. 53 36 1 25 BHT 34 28 30 o i i 1 i 20 10 30 i i 60 50 40 Figure 2. Gas chromatogram of the whole volatile distillate ofNampla. odor was not defined when blended with other components, while Beddows et at. (1979) reported acetic and n-butyric acids as the most abundant and McIver et al. (1982) reported acetic and propionic acids as being present in the highest amounts. In a previous study, Sanceda et al. (1983) showed that the yield of the neutral fraction was the highest followed by the acidic and basic fractions while that of the phenolic 25 34 1 28 53 63 36 BHT ;- 0 .~ ", 10 '" ,--IK --G i 20 "" 30 h" 40 , 50 Figure 3. Gas chromatogram of the whole volatile distillate of Noucmam. , 60 .,. Formation of Volatile Acids during Fermentation ofFish Sauce 45 Table 2. Volatile acids in an aerobically and anaerobically fermented fish sauces (%)" Incubation period, month Aerobic Acids Acetic Propionic Isobutyric Butyric Isovaleric Valerie Isohexanoic n-Hexanoic n-Heptanoic 2.S 0.S4 ± I.S7 ± 0.09 ± 1.84 ± 2.11 ± 0.11 ± 0.08 ± 0.11 ± 0.01 ± 0.01 0.02 0.03 O.OS 0.02 0.03 0.03 0.01 0.01 Anaerobic 12 2.S 1.04 ± 0.01 2.S7 ± O.OS 0.19±0.01 3.11 ± 0.09 2.91 ± 0.04 0.21 ± 0.03 0.17 ± 0.03 0.20 ± 0.01 0.01 ± 0.01 0.31 ± 0.04b 0.19 ± 0.03 b 0.06 ± O.Olh 0.46 ± 0.06 b 1.36 ± O.OSb 0.02 ± 0.01 b O.OS±O.Olb 0.09 ± 0.07 h Ir 12 0.04 0.02 O.OS 0.14 0.98 0.01 O.OS 0.03 ± 0.02 b.c ± O.OOb.c ± 0.01 boc ± 0.0 I boc ± O.OSb.c ± O.Olb.c ± 0.01 b.c ± 0.0 I hoC nd' "Values are means of three replicates. bValues in the anaerobically fermented sauces are significantly different at p - Xem thêm -