Advances in Natural Antioxidants
As he is wont to do, Professor Fereidoon Shahidi, of Memorial University of Newfoundland, somehow managed to cram an encyclopedic overview of the functions of phenolic and amino acid-based antioxidants in foods and health into a 45-minute time frame. Here are just some highlights of his 2017 Clean Label Conference presentation titled “Advances in Naturally Derived Antioxidants for Enhanced Shelflife and Efficacy.”
Antioxidants help to control oxidative processes that deteriorate food quality, while also protecting human tissues from degenerative diseases that account for a majority of global death and morbidity statistics—ergo their popularity.
Particle size, extraction conditions and media used (e.g., water, ethanol) all affect antioxidant quality, as well as whether the desired antioxidants are in free form, esterified form or otherwise bound within the food material matrix. For example, in grains, antioxidants are tightly bound within the outer bran layers.
“Phenolic antioxidants, of which there are more than 7,000, are plant metabolites,” said Shahidi. These, in turn, metabolize into a wide range of other derivatives affecting human physiology, and food and beverage quality. Phenolic antioxidants occur naturally in plants, primarily as natural plant protectors, but also contributing to wound healing and pollinator attraction. In foods and beverages, they act against a range of oxidative reactions that result in off-odors, aromas and colors.
Variables that need to be considered in selecting antioxidants for food and beverage applications include the conditions under which the source materials are grown; the parts of the plant utilized; and processing variables.
Whether the herb or spice is fresh, dried or comminuted plays a role. Particle size, extraction conditions and media used (water, ethanol, acetone, etc.) all affect antioxidant quality. “Length of extraction, processing efficiency and end-product quality do not follow linear relationships,” cautioned Shahidi. Also important are whether the desired antioxidants are in free form, esterified form or otherwise bound within the food material matrix.
This is especially important when dealing with seed and cereal grains in which antioxidants are tightly bound within the outer bran layers. Humans benefit from these bound antioxidants when they are released in the colon during digestion. Thus, bran particle sizes can be very important determinants of antioxidant function and availability.
There are regulatory hurdles that must be navigated: In the U.S., a nutrient content claim can only be made for antioxidants if there exists a Required Daily Intake (RDI) value for the specific antioxidants cited (21 CFR 101.54(g)). In addition, the nutrients claimed “must have recognized antioxidant activity; be present in a quantity sufficient to qualify for the nutrient content claims; and be included as part of the claim” (e.g., “high in antioxidant vitamins C and E”). This is very limiting.
But, antioxidants don’t have to be so-labeled, said Shahidi. De-flavored rosemary, sage and green tea can be added to foods and still be designated as “flavors.” De-flavored mustard seed (a seasoning), when added to comminuted meat at up to 2%, contributes an antioxidant effect similar to nitrite—without affecting the flavor or color of the meat.
Adding green tea extract to fish oil yielded interesting insights: “After seven days, we found that the green tea extract converted into a pro-oxidant,” said Shahidi. The researchers attributed this to the green tea’s chlorophyll. Once stripped of chlorophyll, the extracts were highly effective. Thus, antioxidant effectiveness can depend greatly upon material to which they are added, as well as pre-treatments.
In another example, the primary antioxidant in green tea is epigallocatechin-3-gallate (EGCG). Though highly effective in foods, it does not fully contribute to physiological benefit to consumers, due to its low absorption.
“The bioavailability of highly hydrophilic EGCG is less than 0.1%, because it cannot cross the mitochondrial membranes of cells. When esterified with fatty acids, the antioxidant became highly bioactive. Further work by Shahidi and his colleagues found the lipophilized EGCG esters to exhibit intriguing nutraceutical properties, especially in the treatment of some cancers and hepatitis C, as revealed in cell line studies.
Shahidi closed by citing a new and growing area of interest: antioxidant amino acids. “Animal skins are rich sources of bioactive peptides, once hydrolysed, and quite a number of amino acids exhibit antioxidant properties,” explained Shahidi. “Our laboratory studies have demonstrated significant inhibition of browning using shrimp hydrolyzates at concentrations of 0.5-3.0%. Such amino acids and peptides present a rich, new frontier for clean label development.” Expect many more developments to come.
“Advances in Naturally Derived Antioxidants for Enhanced Shelflife and Efficacy,” Prof. Fereidoon Shahidi, Dept. of Biochemistry, Memorial University of Newfoundland, fshahidi@mun.ca
This presentation was given at the 2017 Clean Label Conference. To download presentations from this event, go to https://cleanlabel.globalfoodforums.com/category/clean-label-rd-academy/
See past and future Clean Label Conference Events at https://cleanlabel.globalfoodforums.com/clean-label-events/
