Abstract
Flaxseed supplementation in diet of dairy cow can effectively enhance the production of ω-3 polyunsaturated fatty acids (n-3 PUFA) in raw milk, which further give rise to the changes of volatile organic compounds (VOCs). In this study, we used headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS) to investigate the VOCs in milk from cows fed three different diets (CK: supplemented with 0 g/d flaxseed; WF: 1,500 g/d whole flaxseed and GF: 1,500 g/d ground flaxseed). A total of 40 VOCs including three acids, six esters, 11 aldehydes, seven alcohols, 13 ketones were identified in all the raw milk samples. Compared with GF supplementation, suppling with WF could influence more compounds in raw milk (GF: five compounds; WF: 22 compounds). Supplementation with WF could increase the concentration of nonanal, heptanal, hexanal, which could cause the occurrence of off-flavors, and reduce the concentration of hexanoic acid (monomer; M), 2-hexanol, ethanol (M), 2-heptanone (dimer; D), 2-pentanone (M), 2-pentanone (D), acetoin (M) in raw milk. GF supplementation in diet could reduce the 2-pentanone (M), 2-pentanone (D). In addition, principal component analysis (PCA) based on the signal intensity of identified VOCs indicated that it is possible to distinguish between the CK and WF milk. However, GF milk could not be distinguished from CK milk. The results demonstrate that compared with GF milk, WF supplementation in diet of dairy cows could increase fishy (heptanal) cardboard-like (pentanal) flavor in milk and decrease sweet (hexanoic acid, 2-heptanone), fruity (ethyl butanoate, ethyl hexanoate, 2-heptanone) flavor which may lead the milk less acceptable. In conclusion, compared with WF, GF supplementation in diet of dairy cow showed higher increase in n-3 PUFA in raw milk, and less influence in VOCs of raw milk and this study might provide theoretical supports for the production of milk rich in n-3 PUFA.
Highlights
Previous reports stated that many factors such as feed [7] and breed [8] can cause variations in the volatile organic compound (VOC) levels in milk
This may due to the difference in analytical instruments between HS-GC-Ion mobility spectrometry (IMS) and HS-SPME GCMS, HSGC-IMS analysis has the potential ability to distinguish between monomers (M) and dimers (D) of target analytes, and dimers may play an important role in distinguishing raw milk from the cows feed different diets
This study demonstrates that the HS-GC-IMS is a useful tool to analyze the raw milk from cows fed different diets
Summary
Previous reports stated that many factors such as feed [7] and breed [8] can cause variations in the volatile organic compound (VOC) levels in milk. For no studies reported the effects of flaxseed supplementation on milk flavor. Owing to its advantages including high sensitivity (ppbv level), ultra-high analytical speed (3–10 s per sample), simplicity and ease of operation at atmospheric pressure (without excessive manual intervention), better separation in two dimensions and color contours image to display the differences among various samples, Headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS) has been widely used for food flavor detection [18], such as for ham [19], garlic [20], honey [21] and rice [22]. Few studies have reported the use of IMS to analyze flavor compounds in raw milk. The aim of this study was to investigate the effects of flaxseed supplementation in diet of cow on VOCs in raw milk. The VOCs in raw milk from the three groups were investigated using headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS). The identification of VOCs in this study provided a theoretical basis for the development of n-3 PUFA-rich milk to exert a variety of beneficial human health effects
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