Pork is the most widely consumed animal meat in the world accounting for approximately 40% of the total global meat intake. Pork almost always undergoes some degree of processing prior to consumption. Consequently, thermal processing induces modification to the 3-dimentional structure of proteins, which may lead to increased digestibility of amino acids (AA).

Protein quality is evaluated in human foods by the digestible indispensable amino acid score (DIAAS) methodology, which can be described as the digestibility of individual dietary indispensable AA (IAA) compared with the same IAA in 1 of the 3 reference protein patterns established by the Food and Agriculture Organization of the United Nations (FAO). Values for DIAAS of bovine meat cooked by various techniques have been determined, yet to our knowledge, there are no reported DIAAS values for pork products and the IAA digestibility of pork after processing has not been reported.

Therefore, the objective for the present work was to determine DIAAS values for pork products, and to test the hypothesis that processing may increase protein quality.

Materials and methods

Nine pork products that underwent different processing techniques were used in the current study. Products included, pork belly processed by 3 different methods: raw belly, smoked bacon, and smoked-cooked bacon, 3 sources of fully-cooked ham: non-cured, alternatively cured with celery salt, and conventionally cured with Prague powder, and pork loin heated to 3 different temperatures: 63^oC, 68^oC, or 72^oC.

Ten gilts (initial BW: 26.63 ± 1.62 kg) were surgically fitted with a T-cannula in the distal ileum and randomly allotted to a 10 × 10 Latin square design with 10 diets and ten 7-d periods with ileal digesta collection for 9 h on d 6 and 7. Pigs were housed in individual pens (2 by 3 m) equipped with smooth plastic siding, partially slatted floors, a feeder, and a nipple drinker. A single pork product was included in 9 of the diets as the only crude protein (CP) and AA containing ingredient, and a N-free diet was also formulated to determine basal endogenous losses of CP and AA. At the conclusion of the experiment, all pork products, the N-free diet, and all ileal digesta samples were analyzed for AA and values for standardized ileal digestibility (SID) were calculated. The DIAAS values were then calculated using the determined concentration of digestible IAA in each pork product and 2 reference protein patterns established by the FAO; 1) children 6 mo to 3 yr and 2) children > 3 yr, adolescents, and adults.

Results

All pork products had a DIAAS value greater than 100 (Table 1), regardless of the reference protein pattern and processing method. When compared with the 2 human AA requirement patterns, Val was the limiting AA in all pork products, except for smoked-cooked bacon, which was limiting in Trp for children 6 mo to 3 yr. For both reference patterns, among the pork bellies, smoked-cooked bacon had the greatest (P < 0.05) DIAAS value with no difference observed between raw belly and smoked bacon. The SID of IAA in smoked-cooked bacon was lower (P < 0.05) than for raw belly (Table 2), but no differences were observed between the other bellies. Among the pork hams, alternatively cured ham had the greatest (P < 0.05) value for DIAAS with no difference observed between conventionally cured and non-cured ham. Alternatively cured and conventionally cured ham had greater (P < 0.05) SID of IAA compared with non-cured ham. The loin heated to 63^oC had a greater (P < 0.05) DIAAS value than the loins heated to 68^oC and 72^oC, with no differences observed between the DIAAS of 68^oC and 72^oC loin, as well as no differences were observed in the SID of IAA among all loins.

Key points

• Pork products are excellent quality proteins with DIAAS values greater than 100.
• DIAAS values greater than 100 indicate the potential of these pork products to complement low quality proteins producing a diet adequate in all IAA.
• Various forms of processing did not negatively affect DIAAS, and curing and moderate heating of pork products may increase protein quality.

Table 1. Standardized ileal digestibility (SID) of amino acid (AA) in ingredients^1,2

¹Data are least squares means of 10 observations per treatment except for smoked bacon, conventionally cured, alternatively cured, and non-cured ham, and 63 ^oC loin that have 9 observations per treatment and for raw belly, 68 ^oC, and 72 ^oC loin that have 8 observations per treatment.

²Standardized ileal digestibility values were calculated by correcting values for apparent ileal digestibility for the basal ileal endogenous losses. Endogenous losses (g/kg of dry matter intake) AA were as follows: crude protein, 14.99; Arg, 0.58; His, 0.22; Ile, 0.39; Leu, 0.66; Lys, 0.58; Met, 0.09; Phe, 0.42; Thr, 0.72; Trp, 0.16; Val, 0.48; Ala, 0.58; Asp, 0.94; Cys, 0.26; Glu, 1.05; Gly, 1.63; Pro, 3.67; Ser, 0.63; Tyr, 0.34.

³Alt. cured = alternatively cured ham.

⁴Conv. cured = conventionally cured ham.

Table 2. Digestible indispensable amino acid scores (DIAAS) of the 9 pork products¹