In the U.S. and most other developed countries, animal-based proteins provide a significant portion of the human diet. However, predictions for animal protein consumption indicates that consumption in Europe and North America will begin to decline by 2035 because plant-based proteins have become accepted as having an appearance, texture, and taste that is close to that of animal products. Examples of plant based proteins that are already on the market are plant-based burgers such as the Impossible Burger and the Beyond Burger, which are produced primarily from soy and pea protein, respectively. The digestible indispensable amino acid score (DIAAS) is recommended by FAO as the best method to determine protein quality in human foods. This method allows for calculation of the protein value of both individual ingredients and combined meals consisting of several proteins. Previous research in our laboratory demonstrated that values for DIAAS obtained in milk and breakfast cereals are additive in mixed meals, and the principle of additivity is believed to be applicable to all types of combined meals, but additional research to demonstrate this is needed. Therefore, the objectives of this experiment were to determine DIAAS values for animal and plant-based burgers and test the hypothesis that DIAAS calculated for a burger and a burger bun are additive in a combined meal.
Experimental Procedures
Ten ileal cannulated gilts (initial body weight: 24.6 ± 1.3 kg) were allotted to a 10 × 6 Youden square design with 10 diets and six 9-d periods. Pigs were housed in individual pens in an environmentally controlled room. The first 7 days of each period were considered the adaptation period to the diet and ileal digesta were collected for 9 h on days 8 and 9 of each period. Six diets contained a burger (80% lean beef, 93% lean beef, 80% lean pork, Impossible Burger or Beyond Burger) or a burger bun as the sole source of crude protein (CP) and amino acids (AA). Three additional diets were prepared by combining one patty (113g) of burger (i.e., 80% lean beef, pork, or Impossible Burger) and a burger bun (90g). A nitrogen-free diet was used to determine basal endogenous losses of AA to enable the calculation of standardized ileal digestibility (SID) of CP and AA. Diet, ingredient and ileal digesta samples were analyzed for CP, AA, and titanium (indigestible marker). The apparent ileal digestibility (AID) and SID of CP and all AA for the ingredients, as well as the measured and predicted AID and SID for the mixed meals, were calculated for children from 6 months to 3 years, and for older children, adolescents, and adults. For the combined meals, DIAAS was also predicted from the individual ingredient DIAAS values.
Results
The SID of CP, His, Ile, Leu, Met, and Val was greater (P < 0.05) in the 93% lean beef, the pork, and the Impossible Burger than in the Beyond Burger (Table 1). The burger bun had lower (P < 0.05) SID of Lys compared with all burgers. The SID of Val and Asx was greater (P < 0.05) in the pork burger than in the 80% lean beef burger, the Beyond Burger, and the burger bun. Regardless of the mixed meal, no differences between the measured and the predicted values for SID of CP and all other AA were observed. For children from 6 months to 3 years and for individuals older than 3 years, the 93% lean beef and pork burgers had greater (P < 0.05) DIAAS compared with the other burgers, whereas the Beyond Burger had the lowest (P < 0.05) DIAAS for all burgers (Table 2). The animal-based burgers had greater (P < 0.05) DIAAS than the plant-based burgers for children between 6 months and 3 years. However, for children older than 3 years, adolescents, and adults, no differences were observed between the 80% lean beef and Impossible Burger, but the 80% lean beef had greater (P < 0.05) DIAAS than the Beyond Burger. The burger bun had lower (P < 0.05) DIAAS compared with all burgers. Regardless of age group and burger-bun combination, there were no differences between the measured and the predicted DIAAS, with the exception that for the combination of pork and burger bun, the DIAAS tended to differ (0.05 ≤ P < 0.10) from zero for individuals older than 3 years (Table 3).
Key points
- The DIAAS in beef and pork burgers are greater than DIAAS in plant-based burgers for both age groups. However, for individuals older than 3 years, the Impossible Burger has DIAAS that is not different from that in the 80% lean beef burger.
- For children from 6 months to 3 years, there was no limiting AA for the animal-based burgers, but for both plant-based burgers the first limiting AA was the sulfur containing AA.
- For individuals older than 3 years, there was no limiting AA for the animal-based burgers or the Impossible Burger, but for the Beyond Burger, the first limiting AA was the sulfur containing AA.
- Burger buns can be low in Lys due to heat damaged caused by overheating when baking.
- The high DIAAS in beef and pork burgers makes it possible to compensate for the low protein quality in burger buns.
- The combination of the Impossible Burger and burger bun does not provide enough digestible AA to meet the requirements for individuals older than 6 months.
- The DIAAS in combined meals of burger and bun is additive and can be predicted from the individual ingredient DIAAS values.
Table 1. Standardized ileal digestibility (SID) of crude protein (CP) and amino acids (AA) in ingredients1
1Values are means and pooled SEs. Labeled means in a row without a common superscript letter differ, P < 0.05. The SID values were calculated by correcting values for AID for the basal ileal endogenous losses. Endogenous losses of AA were calculated from pigs fed the nitrogen-free diet as follows (g/kg DM intake): CP, 24.25; Arg, 1.08; His, 0.22; Ile, 0.32; Leu, 0.50; Lys, 0.53; Met, 0.08; Phe, 0.31; Thr, 0.58; Trp, 0.11; Val, 0.45; Ala, 0.78; Asx, 0.85; Cys, 0.20; Glx, 1.02; Ser, 0.58; Tyr, 0.26.
2n indicates the number of replicates for each item within each treatment.
Table 2. Digestible indispensable amino acid (DIAA) reference ratio and digestible indispensable amino acid scores (DIAAS) in ingredients1
1Values are means and pooled SEs. Labeled means in a row without a common superscript letter differ, P < 0.05. AAA, aromatic amino acid; SAA, sulfur amino acid.
2n indicates the number of replicates for each item within each treatment.
3DIAA reference ratios and DIAAS were calculated using the recommended AA scoring pattern for a child (6 months to 3 years). The indispensable AA reference patterns are expressed as mg AA/g protein: His, 20; Ile, 32; Leu, 66; Lys, 57; SAA, 27; AAA, 52; Thr, 31; Trp, 8.5; Val, 43.
4First-limiting AA in parentheses.
5DIAA reference ratios and DIAAS were calculated using the recommended AA scoring pattern for an older child, adolescent and adult. The indispensable AA reference patterns are expressed as mg AA/g protein: His, 16; Ile, 30; Leu, 61; Lys, 48; SAA, 23; AAA, 41; Thr, 25; Trp, 6.6; Val, 40.
Table 3. Measured and predicted values for digestible indispensable amino acids (DIAA) reference ratio and digestible indispensable amino acid score (DIAAS) in combined meals of burgers and bun1
1Values are means and pooled SEs. Labeled means in a row differ if *Measured vs. predicted, P ≤ 0.05 or **Measured vs. predicted, P ≤ 0.01; or tend to differ if +Measured vs. predicted, 0.05 < P ≤ 0.10. AAA, aromatic amino acid; SAA, sulfur amino acid.
2n indicates the number of replicates for each item within each treatment.
3DIAA reference ratios and DIAAS were calculated using the recommended AA scoring pattern for a child (6 months to 3 years). The indispensable AA reference patterns are expressed as mg AA/g protein: His, 20; Ile, 32; Leu, 66; Lys, 57; SAA, 27; AAA, 52; Thr, 31; Trp, 8.5; Val, 43.
4First-limiting AA in parentheses.
5DIAA reference ratios and DIAAS were calculated using the recommended AA scoring pattern for an older child, adolescent and adult. The indispensable AA reference patterns are expressed as mg AA/g protein: His, 16; Ile, 30; Leu, 61; Lys, 48; SAA, 23; AAA, 41; Thr, 25; Trp, 6.6; Val, 40.