Microbiology, chemistry and quality of fermented fish (Pseudotolithus sp.) lanhouin, and its improvement as a food condiment

Abstract

Lanhouin, a traditionally fermented fish product, widely used as condiment in the Gulf of Benin, is processed by spontaneous fermentation. The socio-economic importance of lanhouin and the processing methods used were investigated through a survey on lanhouin processors and retailers; the quality characteristics of market lanhouin as well as the physico chemical and microbiological changes during the spontaneous fermentation of lanhouin processed in three different occasions were also investigated. The predominant microorganisms were identified and a controlled fermentation using the predominant isolates as starter cultures was carried out. The survey showed that the production and marketing of lanhouin is mainly carried out by women, constituting, for most of them, the main source of income. On the processing procedure, two variants in the method were identified, but both lead apparently to the same final product. Though many types of fish can be used for lanhouin processing, processors preferred cassava fish (Pseudotolithus sp.) followed by lasser African threadfin (Galeoides decadactylus) and king fish (Scomberomorus tritor). Results from the optimization studies indicated that the optimal fermentation conditions were ripening time of 8 hrs, salt concentration of 27.50-30.00 % and fermentation time of 4-5 days. These conditions gave the best quality characteristics of lanhouin in terms of total viable count, sodium chloride and histamine contents. In the course of processing fish into lanhouin, the pH increased from 6.83 to 7.30 and then decreased to 6.98 after 8 days of fermentation. Total volatile nitrogen, free fatty acid and sodium chloride contents of samples increased from 70.50 to 260.15 mg N/ 100 g, 3.60 to 8.15% and 1.50 to 12.05 % after 8 days of fermentation respectively, whilst the moisture content decreased from 73.00 to 46.88 %. Histamine contents (9.05-14.1 mg/100 g) in these samples were lower than the recommended level of 20 mg / 100 g, whilst the majority (75 %) of the market samples contained histamine contents (21.4-39.7 mg/100 g) higher than the maximum allowable level. In general, after a slight increase during the first day of fermentation, the microbial population of the fermenting fish decreased with fermentation time and reached levels of 104 cfu / g after 8 days of fermentation. Bacillus spp. and Staphylococcus spp. were the predominant genera of 3 the lanhouin microbiota and accounted for 48.70 and 27.30% of the total of isolates respectively. Bacillus subtilus, Bacillus licheniformis, Staphylococcus lentus and Staphylococcus xylosus were the dominant species of each genus. The ability of these predominant organisms to ferment fish for controlled fermentation of lanhouin was investigated and the results showed that lanhouin fermentation could be carried out using a single starter culture of Bacillus subtilis and a mixed starter culture of Bacillus subtilis and Bacillus licheniformis as well as a mixed starter culture of Bacillus subtilis and Staphylococcus xylosus. There was a marked difference in the aroma profiles of the spontaneously fermented fish and the fish which was fermented using a starter culture. A total of ninety four aroma compounds were detected in the fish spontaneously fermented for 2, 4, 6 and 8 days. Of these 82 were positively identified with a quality index higher than 70 % and comprised 15 aliphatic hydrocarbons, 6 aromatic hydrocarbons, 9 esters, 9 ketones, 7 acids, 5 alcohols, 9 amines, 2 amides, 7 aldehydes, 2 pyrrole, 6 thiazoles, 2 furan and 3 phenols. The predominant aroma compounds detected over the fermentation period were nitrogen-containing compounds and lipid-derived components. A total of forty one aroma compounds were detected in the inoculated samples of lanhouin. Pyrrole, thiazoles, furan and phenols were not identified in the inoculated samples of lanhouin in contrast to the spontaneous fermentation