Publisher Summary The chapter discusses the stability of proteins and presents the results obtained on small compact globular proteins, which represent one single cooperative system. Protein is a cooperative system and behaves in an all-or-none fashion. Sharp changes in the properties of a protein do not mean anything in themselves because sequential multistep transitions exhibit the same sharp sigmoidal changes in the observed parameters. The problem of stability of native proteins is closely connected with the problem of protein denaturation, as stability can be judged only by breaking the native structure—that is, denaturing protein by various treatments. The pH of the solution is one of the most important factors determining the state of a protein. Potentiometric titration of protein revealed that smooth changes are connected with the titration of groups with a pK not very different from that of free amino acids, while the gross conformational changes associated with pH denaturation are accompanied by the unmasking of buried groups. The chapter also discusses the temperature-induced changes in protein, denaturational and predenaturational changes in protein, thermodynamics of protein unfolding, and thermodynamic properties of protein.

Stability of Proteins Small Globular Proteins

This review defines the range of forms in which cinnamates (p-coumarates, caffeates, ferulates and sinapates) occur in foods and beverages subdividing them into (i) the classic chlorogenic acids and close allies, (ii) other esters, amides and glycosides, and (iii) transformation products formed during processing. Cinnamate derivatives which would not release cinnamic acid by hydrolysis are excluded. The quantitative data are reviewed concisely and attention is drawn to certain shortcomings, in particular a complete absence of data for certain commodities (breakfast cereals, baked goods, tomato products and nuts) and minimal data for pulses, legumes and processed or cooked foods. In addition, more data are required for the edible portion of modern varieties. By extrapolating from such data as are available the important source(s) (i) of individual cinnamates (regardless of the conjugate type) and (ii) of each major class of conjugate, have been identified as follows: (i) Cinnamates: caffeic acid: coffee beverage, blueberries, apples, ciders; p-coumaric acid: spinach, sugar beet fibre, cereal brans; ferulic acid: coffee beverage, citrus juices, sugar beet fibre, cereal brans; sinapic acid: broccoli, kale, other leafy brassicas, citrus juices. (ii) Conjugates: caffeoylquinic acids: coffee beverage, blueberries, apples, ciders; p-coumaroylquinic acids: sweet cherries; feruloylquinic acids: coffee beverage; tartaric conjugates: spinach, lettuce, grapes and wines; malic conjugates: lettuce, spinach, possibly legumes; rosmarinic acid: culinary herbs, mixed herbs, possibly stuffings; cell wall conjugates: spinach, sugar beet fibre, cereal brans. It seems likely that the UK population will fall into several categories depending on (i) their consumption of coffee, (ii) their consumption of bran, and (iii) their consumption of citrus. Those who drink several cups of coffee per day augmented by bran and citrus might easily ingest 500-800mg cinnamates (or even 1 g for the greatest coffee ingest consumption) whereas those who eschew all these and take little fresh fruit or vegetables might struggle to consume 25 mg.

Chlorogenic acids and other cinnamates – nature, occurrence and dietary burden

The structural and mechanical properties of gels formed from biopolymers are discussed both in terms of the techniques used to characterise these systems, and in terms of the systems themselves The techniques included are spectroscopic, chiroptical and scattering methods, optical and electron microscopy, thermodynamic and kinetic methods and rheological characterisation The systems considered are presented in order of increasing complexity of secondary, tertiary and quaternary structure, starting with gels which arise from essentially ‘disordered’ biopolymers via formation of ‘quasicrystalline’ junction zones (eg gelatin, carrageenans, agarose, alginates etc), and extending to networks derived from globular and rod-like species (fibrin, globular proteins, caseins, myosin) by a variety of crosslinking mechanisms Throughout the text, efforts are made to pursue the link (both from experiment and from theory) between the structural methods and mechanical measurements As far as we are aware this is the first major Review of this area since that of J D Ferry in 1948 — The interest shown by polymer physicists in more complex biochemical systems, and the multi-disciplinary approaches now being applied in this area, make the format adopted here, in our opinion, the most logical and appropriate

Structural and mechanical properties of biopolymer gels

This paper summarises the occurrence in foods and beverages of the cinnamic acids, their associated conjugates and transformation products. Quantitative data are lacking for some commodities known to contain them, but it is clear that for many people coffee will be the major source. The daily dietary intake of total cinnamates may vary substantially from almost zero to perhaps close to 1 g. The data relating to their absorption and metabolism are presented along with a consideration of their possible in vivo effects. Data for true bioavailability are incomplete: in particular it is not clear whether availability differs markedly with the form of the conjugate, and whether as a consequence some dietary sources may be superior to others.

Chlorogenic acids and other cinnamates - nature, occurrence, dietary burden, absorption and metabolism

There is growing recognition that many phenolic secondary metabolites present in foodstuffs may possibly exert beneficial effects on human health. This may to some degree be mediated via antioxidant actions, but a range of more specific pharmacological effects have also been proposed. Given this background, there may be favourable consequences for the general health of Western populations as a result of optimising the phenolic content of the diet. This paper reviews what is known of the function of phenolics both in the plant and in man. It also describes current understanding of the biosynthesis of phenolics in plants, with emphasis on where potential controlling steps may exist. Finally, advances in identification and isolation of the genes coding for phenolic biosynthetic enzymes or regulatory proteins are also summarised. Taken together, this information provides a basis for attempts to modify and optimise the phenolic content of food crops, using either conventional plant breeding along with manipulation of agronomic practices, or else the more targeted approaches of modern molecular biology.



© 2000 Society of Chemical Industry

Phenols in the plant and in man. The potential for possible nutritional enhancement of the diet by modifying the phenols content or profile

alpha-Glucosidase inhibitory activity was found in aqueous methanol extracts of tochu-cha, dried leaves of Eucommia ulmoides (Eucommiaceae). Five active principles against yeast enzyme were isolated and characterized. Among them, quercetin (1, Ki: 8.5 x 10(-6) M) was considered to contribute mostly to the activity of the tochu leaves. In regard to an animal alpha-glucosidase, rat intestinal sucrase activity was also inhibited by 1.

Isolation and Identification of α-Glucosidase Inhibitors from Tochu-cha (Eucommia Ulmoides)

Five antioxidative caffeoylquinic acid derivatives were isolated from the roots of burdock (Arctium lappa L.), an edible plant in Japan. Their structures were established as 1-O-,5-O-dicaffeoylquinic acid (1), 1-O-,5-O-dicaffeoyl-3-O-succinylquinic acid (2), 1-O-,5-O-dicaffeoyl-4-O-succinylquinic acid (3), 1-O-,5-O-dicaffeoyl-3-O-,4-O-disuccinylquinic acid (4), and 1-O-,3-O-,5-O-tricaffeoyl-4-O-succinylquinic acid (5) on the basis of chemical and spectral (NMR, MS) evidence. The antioxidant activities were measured in a hexane/2-propanol solution of methyl linoleate in the presence of a radical initiator. The antioxidant efficiency increased in the order of α-tocopherol < chlorogenic acid < caffeic acid < (1) = (2) = (3) = (4) < (5).

Antioxidative caffeoylquinic acid derivatives in the roots of burdock (Arctium lappa L.)

A phenolic amide, N-p-coumaroyltyramine (1), was isolated as an α-glucosidase inhibitor from methanol extracts of Welsh onion (Allium fistulosum). The inhibitory activity of 1 against a yeast enzyme was as high as Ki 8.4 × 10−7 m. From a structure-activity relationship study of 1 and its related compounds, the occurrence of α-glucosidase inhibitory activity required a p-coumaramide structure, with an amide hydrogen and alkyl or aralkyl substituent on the amide part.

Isolation and Activity of N-p-Coumaroyltyramine, an α-Glucosidase Inhibitor in Welsh Onion (Allium fistulosum)

An aqueous methanol extract from green tea showed potent acetyl-CoA carboxylase inhibitory activity. An active compound was isolated from the extract and identified as (-)-epigallocatechin gallate by instrumental analyses. The IC50 value of (-)-epigallocatechin gallate was 3.1×10-4 M. Among tea catechins and related compounds, nearly equal activity was found in (-)-epigallocatechin gallate and (-)-epicatechin gallate, whereas (+)-catechin, (-)-epicatechin, (-)-epigallocatechin, gallic acid and methyl gallate each had no inhibitory activity. These results indicate that the 3-O-gallate group of the catechin structure was necessary for this activity. (-)-Epigallocatechin gallate inhibited triglyceride accumulation in 3T3-L1 cells at a concentration of 1.0×10-7 M or higher.

https://www.tandfonline.com/doi/pdf/10.1271/bbb.62.532

Ryoya Niki

Papers

Isolation and Identification of α-Glucosidase Inhibitors from Tochu-cha (Eucommia Ulmoides)

Antioxidative caffeoylquinic acid derivatives in the roots of burdock (Arctium lappa L.)

Isolation and Activity of N-p-Coumaroyltyramine, an α-Glucosidase Inhibitor in Welsh Onion (Allium fistulosum)

Isolation and Identification of Acetyl-CoA Carboxylase Inhibitors from Green Tea (Camellia sinensis)

Micellar structure of β-casein observed by small-angle X-ray scattering