Bioavailability of B-6 vitamers from thermally processed milk and ground beef

Arunabala Pingali, Purdue University

Abstract

The extent of protein binding and the changes in vitamin B-6 composition that occur between collection and pasteurization was investigated in intrinsically labeled $\lbrack\sp{14}\rm C\rbrack$ milk expressed from rats on the 10th day of lactation. Milk was stored for 1, 5 and 10 days at $4\sp\circ$C after collection and pasteurized at $62.5\sp\circ$C for 30 mins at each storage period. Results indicated that 99% of the B-6 vitamers were unbound. Pyridoxal 5$\sp\prime$-phosphate (PLP) was the predominant vitamer in raw and pasteurized milk even after 10 days of storage. During storage, PLP content gradually decreased, partly accounted for, by the increase in pyridoxal (PL) content. No significant 4-pyridoxic acid (4-PA) was produced after storage and/or pasteurization indicating that vitamin B-6 activity was not lost during storage or pasteurization. To assess the effect of heat sterilization of milk on vitamin B-6 composition and bioavailability, rats were orally administered $\lbrack\sp3\rm H\rbrack$pyridoxine (PN), $\lbrack\sp3\rm H\rbrack$4-PA or $\lbrack\sp3\rm H\rbrack$PL in water, or $\lbrack\sp3\rm H\rbrack$PL in fresh milk with or without subsequent sterilization at $120\sp\circ$C for 20 min. $\lbrack\sp3\rm H\rbrack$PL in sterilized milk underwent partial conversion to pyridoxamine (PM) and 4-PA, as well as irreversible binding to protein. $\lbrack\sp3\rm H\rbrack$PL in water and unheated milk was well absorbed and similar to $\lbrack\sp3\rm H\rbrack$PN. The intestinal absorption of $\sp3\rm H$ from sterilized milk and $\lbrack\sp3\rm H\rbrack$4-PA was significantly reduced compared to $\lbrack\sp3\rm H\rbrack$PN or $\lbrack\sp3\rm H\rbrack$PL. Thus, vitamin B-6 activity in sterilized milk was reduced due to irreversible binding to protein and partial formation of 4-PA. The relative bioavailability of vitamin B-6 from cooked beef supplemented with PL or PM was investigated in two groups (n = 6) of healthy young men fed an isocaloric diet for two alternate test periods i.e., weeks 1 and 4. After 2 days of acclimation, subjects ingested (5.98 umol) PL or (5.95 umol) PM in apple juice and cooked beef ($350\sp\circ$F, 75 mins) during subsequent test periods. After vitamin B-6 dosage, 24-hr urine samples were collected for two days. Urinary 4-PA excretion during 24-hr was not significantly different between the groups fed the cooked test samples. Vitamin B-6 bioavailability from cooked beef was high despite increased irreversible binding of B-6 vitamers to components of beef.

Degree

Ph.D.

Advisors

Trumbo, Purdue University.

Subject Area

Nutrition

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