Influence of acid hydrolysis, saponification and sample clean‐up on the measurement of phytosterols in dairy cattle feed using GC–MS and GC with flame ionization detection

Abstract

The fortification of processed foods including dairy products is increasingly commonplace with phytosterols among many compounds used to improve the nutritional value of food products. It is also increasingly common practice for some dairy cattle feeds to be fortified for their potential to increase phytosterol levels in milk. In this study, a combined, streamlined protocol using acid hydrolysis, saponification and sample clean-up was developed to enable the rapid and reliable measurement of phytosterols. The method was developed with focus on streamlining the overall technique to make it suitable for commercial laboratories, to reduce labor and consumable costs, while maintaining accuracy. A total of 12 different feed types commonly used in the dairy industry were analyzed with the highest and lowest sterol contents found in cotton seed oil and tannin with average phytosterol contents of 256 and <30 mg per 100 g, respectively. With a limit of reporting of 30 mg/kg for individual sterols and a correlation coefficient > 0.99, the method was validated for milk to enable feed comparison studies with respect to the total phytosterol content in raw milk.

Modification of the sterol profile in milk through feeding

“…Other plant sterols detected in the milk samples included campesterol and β-sitosterol but at minor or trace levels. In a recent study, the phytosterol content in the cattle feed used for this present study, lanosterol, and lathosterol were not detected (Duong et al, 2018). Given that both lanosterol and lathosterol were found in the milk, it suggested that their presence in milk was a result of endogenous synthesis.…”

“…It was observed that the mean lanosterol content was highest in the milk from the animals fed on the control diet and lowest in the milk from those feds on the DGM feed; however, this was not reflected in the cholesterol results for the different feed types. Examination of the phytosterol content in the respective diets showed that the control diet contained the lowest amount of phytosterols, with 4,254 mg compared with the WGM and DGM, which contained 9,922 mg (Duong et al, 2018). The results suggest that high phytosterol levels may affect the endogenous synthesis of lanosterol, because this is generally observed in human subjects ingesting a high plant sterol diet (Ostlund, 2002;Kritchevsky and Chen, 2005).…”

“…A comparison of total phytosterol content in the feed at the 13.5 kg of DM rate was 13,200, 12,300, and 13,500 mg for the control, PSE2a, and PSE2b, respectively, with trace levels of cholesterol (Duong et al, 2018). This experiment suggests that the addition of protein into the feed in the form of solvent-extracted canola meal may increase the levels of cholesterol and lanosterol in the milk produced when compared with the PSE2a milk.…”

“…The milk and cattle feed were analyzed for their phytosterol content as per the method described by Duong et al (2018). In brief, 5 mL of thawed milk was spiked with a surrogate standard (5β-cholestan-3α-ol), followed by the addition of 5 mL heptane, which was then hydrolyzed using hydrochloric acid (4 mL of 8 M).…”

Analysis of Phytosterols Content in Italian-Standard Espresso Coffee

“…However, through EC preparation, just PS in the free form are extracted. Indeed, various studies reported that the extraction of conjugated PS in food matrix requires a prior hydrolysis step in acidic conditions to break down ether and ester bonds linking PS in plant cell membranes [31,32].…”