Using Fluorescence Spectroscopy To Identify Milk from Grass-Fed Dairy Cows and To Monitor Its Photodegradation

Abstract

Owing to its high ω-3 fatty acid content, milk from grass-fed dairy cows is becoming increasingly more attractive to consumers. Consequently, it is important to identify the origins of such products and to measure their content, at least relative to some standard. To date, chromatography has been the most extensively used technique. Sample preparation and cost, however, often reduce its widespread applicability. Here, we report the effectiveness of fluorescence spectroscopy for such quantification by measuring the amount of chlorophyll metabolites in the sample. Their content is significantly higher for milk from grass-fed cows compared to milk from grain/silage-fed cows. It is 0.11-0.13 μM in milk samples from grass-fed cows, whereas in milk from cows fed grain/silage rations, the concentration was 0.01-0.04 μM. In various organic milk samples, the chlorophyll metabolite concentration was in the range of 0.07-0.09 μM. In addition, we explored the mechanisms of photodegradation of milk. Riboflavin and chlorophyll metabolites act as photosensitizers in milk for type-I and type-II reactions, respectively. It was also observed that the presence of high levels of chlorophyll metabolites can synergistically degrade riboflavin, contributing to the degradation of milk quality.

Evaluation and quantification of associations between commonly suggested milk biomarkers and the proportion of grassland-based feeds in the diets of dairy cows

“…Another explanation for the green color of our milk samples could be pigments like chlorophyll metabolites, including pheophorbide a . Bhattacharjee et al [ 40 ] demonstrated that commercial milk from grass-fed cows was richer in chlorophyll metabolites than milk from grain/silage-fed cows.…”

The degradation of chlorophyll pigments in dairy silage: the timeline of anaerobic fermentation

“…Each solution was placed in a dark room for 24 h to ensure the full extraction of the pigments to the solvent. The absence of light ensures that the chlorophyll in the solution does not undergo photodegradation 1 . In order to correct for variable water content in the frozen silage, for each sample, three portions of about 5 g per portion, from various areas of the frozen sample were ground to a homogeneous consistency, weighed and then placed in an oven to dry for 24 h in order to obtain a dry‐to‐wet mass ratio.…”

“…Our current investigation began as a consequence of a previous project 1 focusing on authenticating the grass‐fed label by analyzing chlorophyll catabolite 2 content in milk and correlating that to the cattle‐diet, specifically those which are either grass or derived from grass. These studies were carried out by measuring the fluorescence of chlorophyll and its derivatives 3–5 in the milk 1 . Detection of a strong signal from chlorophyll metabolites in the milk was suggested to be indicative of a grass‐fed diet.…”

“…This color change occurs as the amount of lactic acid increases during the fermentation process, thus decreasing the pH 8,11,12 with degradation of the plant pigments. Our previous study 1 showed that the detection of chlorophyll metabolites was affected by the prolonged exposure of the milk sample to light as well as the diet of the animals. Based upon the variation in fluorescence signals in milk from cows fed different diets, we observed that silage diets produced lower signals in milk.…”

Spectroscopic technologies and data fusion: Applications for the dairy industry

“…Given current awareness regarding product origin and traceability in the dairy industry, a rapid technique based on fluorescence and riboflavin could be useful in confirming product authenticity. Fluorescence has also been used to authenticate milk from grass-fed cows ( 89 ). The levels of riboflavin and chlorophyll metabolites were measured in the milk and shown to be significantly higher in grass-fed cows than in grain or silage-fed cows, most likely due to the higher level of chlorophyll in fresh grass.…”