The in vitro digestibility of beef varies with its inherent ultimate pH

Abstract

Animal carcasses and cuts of meat are usually differentiated and valued according to size and compositional attributes. An underappreciated variable of red meat is its inherent ultimate pH (pH_u) value, which affects organoleptic and processing characteristics. This study tests the hypothesis that high pH_u aged meat would be more digestible than low pH_u unaged (fresh) meat. Longissimus dorsi muscles collected from 59 bull carcasses had pH_u values of 5.6–6.9. These were aged for 21 days at −1.5 °C, then raw and cooked (72 °C) samples were enzymatically digested at 37 °C with pepsin (pH 1.9 for 90 min) followed by pancreatin (pH 8.0 for an additional 120 min) to simulate conditions in the stomach and small intestine, respectively. Meat proteins and peptides in the digests were separated by 1D SDS PAGE. Regardless of pH_u, ageing or cooking, most sarcoplasmic and myofibrillar proteins were rapidly digested by pepsin, with concomitant release of products identified by LC-MS/MS as mainly myosin-1, -2 and -7, α-actinin-2 or -3 and tropomyosin beta and alpha chains. These products were resistant to further digestion for the entire 210 min duration of the incubation. In terms of rate and extent of digestibility of these resistant products, high pH_u > low pH_u (P < 0.001), whereas aged > unaged (P < 0.003), with the effect of cooking dependent on pH_u and varying somewhat by protein. Overall, the digestibility of meat samples increased with increasing pH_u (P < 0.001). Beef meat was highly digestible but could be further differentiated on the basis of its pH_u and the ease of digestibility of proteins. Specific carcasses or cuts could be targeted to consumer groups in order to provide benefits and add value.