Fermented coconut may produce natural flavour compounds
The study, published in the International Journal of Food Microbiology, suggests the products from coconut cream fermentation by the yeast Kluyveromyces lactis KL71 (K. lactis) could be used as novel flavouring bio-ingredients for in food products.
“This study has demonstrated the feasibility of producing a sulphur flavour concentrate by yeast fermentation of coconut cream supplemented with L-methionine,” wrote the researchers, led by Dr. Shao-Quan Liu, from the National University of Singapore.
“This low-cost, natural flavour bioingredient may find applications in foods such as meats, savoury flavour, soups and imitation cheeses,” they added
Flavour compounds
Volatile sulphur flavour compounds (VSFCs) occur in fruits, breads, beers and fermented soybean products, and contribute a wide variety of distinct flavours that can be found in many foods and beverages.
Methionol is a potent VSFC that has a powerful sulphur- like odour described by the authors as “soup-like, meaty, boiled potato, vegetable, savoury or toasted cheese.”
Methionol is regarded as an off-flavour compound in beer and wine, but is considered as an important component of the aroma profiles in cheeses, particularly in high quality cheddar and camembert
Researchers noted that producing VSFCs from natural sources is a challenge because in general, only very low amounts are formed from any one source. However, recent research has found relatively high concentrations of methionol can be produced naturally through the fermentation of yeast in dairy media.
The new research investigated the production of methionol – and other VSDCs – from yeast fermentation in coconut cream.
Optimal production
Eight yeasts were found to produce methionol in coconut cream – with S. cerevisiae showing the highest production, followed by yeast K. lactis.
Relative to S. cerevisiae and K. lactis yeasts, the other six yeasts were reported to produce near negligible levels methionol.
In addition to methionol, the eight yeasts produced trace amounts of various other VSFCs, including 3-methylthio-1-propene, 3-methylthio-1-propyl acetate, and 3-methylthio-1-propanal. Of these, methional, methionol and phenylethyl acetate were found to have the highest odour potency.
The authors reported that the fermentation of the yeast S. cerevisiae for the production of methionol has been the focus of other research, whilst K. lactis KL71 has received “little attention.” Therefore researchers focused further studies on the fermentation of K. lactis KL71 under different culture conditions.
The highest methionol production was found in coconut cream adjusted to pH 5.0, with a 57 per cent increase in methionol compared to pH-unadjusted coconut cream.
The optimum temperature for production was determined to be 33 °C, whilst linear increases in production were observed as L-methionine concentration increased from 0.05 per cent to 0.15 per cent, where they reached optimum levels and began to level off.
Food applications
“The product of coconut cream fermentation by Kluyveromyces lactis KL71 may be considered as a novel, plant-based, natural and complex flavouring bioingredient in food applications,” concluded the researchers.
They also noted 2-Phenylethyl acetate was found to have odour thresholds close to that of methionol. “Described as having a floral, rose-like, and sweet odour, its importance in the overall odour perception […] should not be overlooked.”
However, the authors added that further work into the fermentation of yeasts to produce such flavours would be required, including “full optimization, scale-up and costing of the process.”
Source: International Journal of Food Microbiology
Volume 143, Issue 3, Pages 235-240, doi: 10.1016/j.ijfoodmicro.2010.08.003
“Production of flavour-active methionol from methionine metabolism by yeasts in coconut cream”
Authors: Y.X. Seow, P.K.C. Ong, S.Q. Liu
