As interest in the cholesterol-lowering ingredients increases, researchers from the University of Manitoba have reported that, contrary to previous reports, phytosterols do not possess antimicrobial activity, which could detrimentally affect yoghurts. "The commercial phytosterol preparation had no effect on growth and acid development by Lactobacillus bulgaricus and Streptococcus thermophilus during yogurt production at 33 degrees Celsius and storage at four degrees Celsius for 30 days," wrote the authors in the Journal of Food Science.
"This is seen as a beneficial feature since growth and acid development by these organisms are crucial for yogurt quality." The study has implications for food formulators wishing to tap into the use of phytosterols in a wider range of food products, beyond the established margarine and milk.
Phytosterols, cholesterol-like molecules derived from plants, are increasingly well known to consumers due to their scientifically proven ability to reduce cholesterol levels. As consumer awareness has increased, the number of products containing plant sterols or plant stanols and their esters has increased. "Since increased interest is focused on the incorporation of phytosterols in dairy-based products, the objectives of the present study were to investigate the antimicrobial activity of phytosterols in milk and their effect on the growth and survival of starter cultures and potential spoilage organisms in yogurt," explained the researchers.
A recent Frost and Sullivan report valued the European market at €146m ($184.6m) in 2005, and estimates this to reach €312.5m ($395.2m) in 2012, an increase of 114 per cent. The researchers, led by Greg Blank, used a commercial phytosterol preparation (CPP) from Forbes Medi-Tech containing beta-sitosterol, campesterol, sitostanol, and campestanol in pasteurised milk with starter cultures to produce yoghurt. The phytosterols were added in concentrations ranging from 0.26 to 1.8 per cent.
No antimicrobial activity was observed by the researchers, showing that phytosterols could be employed in combination with yoghurt starter cultures. On the other hand, when the CPP was dispersed in combination with sodium stearoyl lactylate (SSL) an effect on bacterial counts, which was not due to the presence of SSL, said the scientists.
"While the CCP was somewhat antimicrobial when formulated with dispersing agents, it otherwise had no antimicrobial activity," they said. "Although the addition of CPP did not detrimentally affect the quality of yogurt, neither did it increase the shelf life by inhibiting the growth of typical spoilage microorganisms," added the researchers.
Clinical trial support for health benefits Numerous clinical trials in controlled settings have reported that daily consumption of 1.5 to 3 grams of phytosterols/-stanols from foods can reduce total cholesterol levels by eight to 17 per cent, representing a significant reduction in the risk of cardiovascular disease, but the majority of studies have looked at high-fat products as carriers for the sterols.
High cholesterol levels, hypercholesterolaemia, have a long association with many diseases, particularly cardiovascular disease (CVD), the cause of almost 50 per cent of deaths in Europe, and reported to cost the EU economy an estimated €169bn ($202bn) per year. The new study was partly financed by Forbes Medi-Tech and the Natural Sciences and Engineering Research Council of Canada (NSERC).
Source: Journal of Food Science (Blackwell) Published online ahead of print, Online Early, doi:10.1111/j.1750-3841.2008.00668.x "Phytosterol Effects on Milk and Yogurt Microflora"
Authors: E. Monu, G. Blank, R. Holley, J. Zawistowski