The research could have implications for both dairy and fortified dairy, with the potential to prolong shelf-life and quality of the products.
In the UK, skimmed milk is growing in popularity, and accounts for about 14 per cent of total milk sales. Milk contains 15 vitamins and minerals, including significant amounts of calcium, vitamin D, riboflavin and vitamin B12.
However, the riboflavin content is susceptible to oxidation by light. The oxidation products of this process can then destroy other vitamins in the milk, leading to a significant loss of nutritional quality.
Writing in the Journal of Agricultural and Food Chemistry, lead author Mariana Montenegro from Universidad Nacional de Santiago del Estero in Argentina and her co-workers report that by encapsulating small amounts of lycopene in gum arabic and sucrose, the resulting microcapsules can protect the riboflavin against photo-oxidation.
Microcapsules are tiny particles that contain an active agent or core material surrounded by a shell or coating, and are now increasingly being used in food ingredients preparation.
The researchers focused on the riboflavin (Rf)-mediated degradation of vitamins A and D3, with the vitamin A and D3 content of the commercial skimmed milk powder being 0.6 and 4.3 milligrams per litre, respectively.
The microcapsules were produced using the spray-dried technique, the most commonly used technology in the food industry because of the low costs and availability of equipment.
Using fluorescent white lights, the researchers tested the photo-degradation of riboflavin, vitamin A and vitamin D3 in standard skimmed milk, and the skimmed milk containing the lycopene microcapsules.
"The addition of lycopene microencapsulated by spray-drying with a gum arabic-sucrose (8:2) mixture (MIC) produced a reduction of ca. 45 per cent in the photosensitized degradation rate of both vitamins," wrote the researchers.
"These results show the functional ability of gum-arabic based microcapsules to act as antioxidant species in food systems and that the microencapsulation spray-drying process does not affect the excellent [singlet molecular oxygen] quencher lycopene ability," they said.
Low lycopene contents were used so that the colour of the milk was not significantly modified.
"In summary, the photosensitized riboflavin-mediated degradation of vitamins A, D3, and Rf itself in skimmed milk can be strongly reduced by the addition of small amounts of lycopene-gum arabic-sucrose microcapsules, without modification of the bulk properties of skimmed milk," they concluded.
The study was funded by the funding agencies CONICET, CICyT-UNSE, and Fundacion Antorchas of Argentina, FAPESP and CNPq of Brazil, and DSM Nutritional Products of Switzerland.
Source: Journal of Agricultural and Food Chemistry ASAP Article, published on-line ahead of print; doi: 10.1021/jf0622883 "Photoprotection of Vitamins in Skimmed Milk by an Aqueous Soluble Lycopene-Gum Arabic Microcapsule" Authors: M.A. Montenegro, I.L. Nunes, A.Z. Mercadante, and C.D. Borsarelli