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Reaction Kinetics in Food Systems
Published in Dennis R. Heldman, Daryl B. Lund, Cristina M. Sabliov, Handbook of Food Engineering, 2018
Ricardo Villota, James G. Hawkes
Riboflavin, or vitamin B2 (also referred to as vitamin G, lactoflavine, and chemically as 7,8-dimethyl-10-(1′-ribityl) isoalloxazine), is a precursor of the flavin cofactors, FAD (flavin adenine dinucleotide [riboflavin-5′-trihydr ogen-diphosphate]) and FMN (flavin-mononucleotide [riboflavin-5′-monophosphate]), which function in many important enzymatic redox reactions in intermediary metabolism (Figure 3.12). Riboflavin exists in dietary sources predominantly in the form of its coenzyme derivatives, FAD and FMN, which in turn can carry out one- and two-electron transfer reactions involved in diverse biochemical catalytic reactions. Henriques et al. (2010) have presented an overview of many of the updated riboflavin biochemical mechanisms, with particular emphasis on deficiencies of the vitamer and their implications on fatty acid metabolism. The actual free form of riboflavin is more frequently found in commercial multivitamin applications. Common biological sources of B2 are similar to most of the other B-vitamins, including eggs, milk, cheese, meats (liver and kidneys), yeast, and leafy green vegetables. From a nutritional perspective, it should be pointed out that, although green plants can synthesize their own free riboflavin and mammals cannot, the relative amounts found in meat sources (as NAD and FMN) are significantly higher than totals found in most plants. In that FAD and FMN occur chiefly in non-covalently-bound forms to enzymes, while covalently-bound flavins are less available for absorption, are all factors to consider when carrying out vitamer analyses. More detailed reviews of the biochemical function of the flavins have been published (Powers, 2003; Henriques et al.; 2010; Pinto and Rivlin, 2014). Riboflavin is relatively stable in foods under ordinary conditions, as long as it is not exposed to light. It has relatively low water solubility (0.067–0.333 mg/ml) and exhibits a fluorescent yellow-green color (Merck, 2002), which can limit its ability for fortification from a visual perspective, although it may be used as a food colorant with potential health benefits (Table 3.4). FMN has slightly higher solubility and may be a better choice for liquid applications; however, color may still be an issue, as this is also used as a colorant in Europe (E101a). Stability of riboflavin is pH dependent, being more stable under acidic conditions, with maximum stability to heat being between pH 2.0 and 5.0 and destruction of the isoalloxazine ring at pH > 7.0 (Ball et al., 1994). With regard to FAD and FMN, they are both readily converted to riboflavin at pH < 5.0 (Russell and Vanderslice, 1990). This factor is actually used as a prestep when analyzing for total riboflavin; however, it should be avoided if analyzing for each of the three vitamers individually.
The effect of freeze-drying and storage on lysozyme activity, lactoferrin content, superoxide dismutase activity, total antioxidant capacity and fatty acid profile of freeze-dried human milk
Published in Drying Technology, 2022
Dorota Martysiak-Żurowska, Patrycja Rożek, Małgorzata Puta
The lyophilization process can also be successfully used to dehydrate human milk. The effects of freeze-drying on the concentrations of fat, triglycerides, fatty acids (FAs), proteins, glucose, polyphenols, lipase, B-vitamins, vitamin C, catalase (CAT), lysozyme (LZ), oligosaccharides and immunoglobulins as well as total antioxidant capacity (TAC) and lipid peroxidation in human milk have been evaluated by numerous authors in studies analyzing the consequences of food processing operations.[15–20] The potential use of freeze-dried human milk as a nutritional supplement for infants, in particular preterm neonates, has also been researched.[21,22]