Phytosterols, phytostanols, and their conjugates in foods: structural diversity, quantitative analysis, and health-promoting uses

Sterols are vital components of all eukaryotic cells. This review describes the variety of sterol structures found in microalgae, yeasts, fungi, protozoans and microheterotrophs. Reports of the occurrence of sterols in prokaryotic cells are critically assessed. Methylotrophic bacteria contain unusual 4-methylsterols, but reports of 4-desmethyl sterols in cyanobacteria and other bacteria are limited and many of these seem dubious. Possible application areas for sterols derived from mass culture of microalgae and other microorganisms are highlighted.

Sterols in microorganisms.

Wheat is the most important staple crop in temperate zones and is in increasing demand in countries undergoing urbanization and industrialization. In addition to being a major source of starch and energy, wheat also provides substantial amounts of a number of components which are essential or beneficial for health, notably protein, vitamins (notably B vitamins), dietary fiber, and phytochemicals. Of these, wheat is a particularly important source of dietary fiber, with bread alone providing 20% of the daily intake in the UK, and well-established relationships between the consumption of cereal dietary fiber and reduced risk of cardio-vascular disease, type 2 diabetes, and forms of cancer (notably colo-rectal cancer). Wheat shows high variability in the contents and compositions of beneficial components, with some (including dietary fiber) showing high heritability. Hence, plant breeders should be able to select for enhanced health benefits in addition to increased crop yield.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/fes3.64

The contribution of wheat to human diet and health

Polyphenolic phytochemicals are ubiquitous in plants, in which they function in various protective roles A 'recommended' human diet contains significant quantities of polyphenolics, as they have long been assumed to be 'antioxidants' that scavenge excessive, damaging, free radicals arising from normal metabolic processes There is recent evidence that polyphenolics also have 'indirect' antioxidant effects through induction of endogenous protective enzymes There is also increasing evidence for many potential benefits through polyphenolic-mediated regulation of cellular processes such as inflammation Inductive or signalling effects may occur at concentrations much lower than required for effective radical scavenging Over the last 2-3 years, there have been many exciting new developments in the elucidation of the in vivo mechanisms of the health benefits of polyphenolics We summarise the current knowledge of the intake, bio-availability and metabolism of polyphenolics, their antioxidant effects, regulatory effects on signalling pathways, neuro-protective effects and regulatory effects on energy metabolism and gut health

Polyphenolic phytochemicals--just antioxidants or much more?

Although traditionally used as a valuable health supporting nutrient, the vegetative parts of Opuntia spp. plants are scarcely used in modern nutrition and medicine. While all kinds of different Opuntia spp. have been studied, a systematic approach regarding the inter-relationships between the composition and the pre- and postharvest conditions is still missing. Therefore, the present review compiles and discusses literature on the chemical composition of cactus stems, the knowledge on uses in food, medicine, and cosmetics. It is concluded that much research is needed to get an insight into the multitude of bioactivities reported in the traditional literature but also to take advantage of the respective constituents for food and pharmaceutical applications.

Cactus stems (Opuntia spp.): A review on their chemistry, technology, and uses

Plant sterols are an essential component of the membranes of all eukaryotic organisms. They are either synthesised de novo or taken up from the environment. Their function appears to be to control membrane fluidity and permeability, although some plant sterols have a specific function in signal transduction. The phytosterols are products of the isoprenoid pathway. The dedicated pathway to sterol synthesis in photosynthetic plants occurs at the squalene stage through the activity of squalene synthetase. Although the activity of 3-hydroxymethyl-3-glutaryl coenzyme A (HGMR) is rate-limiting in the synthesis of cholesterol, this does not appear to be the case with the plant sterols. Up-regulation of HGMR appears to increase the biosynthesis of cycloartenol but not the Δ5-sterols. A decline in sterol synthesis is associated with a suppression of squalene synthetase activity, which is probably a critical point in controlling carbon flow and end-product formation. The major post-squalene biosynthetic pathway is regulated by critical rate-limiting steps such as the methylation of cycloartenol into cycloeucalenol. Little is known about the factors controlling the biosynthesis of the end-point sterol esters or stanols. The commonly consumed plant sterols are sitosterol, stigmasterol and campesterol which are predominantly supplied by vegetable oils. The oils are a rich source of the steryl esters. Less important sources of sterols are cereals, nuts and vegetables. The nutritional interest derives from the fact that the sterols have a similar structure to cholesterol, and have the capacity to lower plasma cholesterol and LDL cholesterol. Since the morbidity and mortality from cardiovascular disease have been dramatically reduced using cholesterol-lowering drugs (statins), the interest in plant sterols lies in their potential to act as a natural preventive dietary product. Stanols (saturated at C-5) occur in low amounts in the diet and are equally effective in lowering plasma cholesterol and do not cause an increase in plasma levels, unlike the sterols which can be detected in plasma.

© 2000 Society of Chemical Industry

Plant sterols: biosynthesis, biological function and their importance to human nutrition.

The NEODIET concerted action, funded under the EU FAIR programme, has focussed for the past two years on evaluating the strategies for the improvement of the nutritional quality of plant foods. These strategies involve the enhancement of key metabolites through the application of conventional plant breeding and genetic engineering, as well as the application of newer approaches to food processing. This paper focuses on the benefits of improving the nutritional quality of plants by the enhancement of the beneficial phytochemicals directly in the plant rather than by the addition of essential nutrients to processed foods as has been conventionally undertaken. Examples of the disadvantages of fortifying plant foods are given. The role of food technology in improving the bioavailability of some nutritional constituents, and thereby improving the overall quality of the food, is illustrated with reference to the carotenoids. The importance of structure of the plant metabolite in determining nutritional quality is also illustrated with reference to the effects of structure on the bioavailability and biological effectiveness of plant flavonoids.

David G Lindsay

Papers

Plant sterols: biosynthesis, biological function and their importance to human nutrition.

The Nutritional Enhancement of Plant Foods in Europe ‘NEODIET’

Dietary anticarcinogens and antimutagens—chemical and biological aspects