A multienzyme methodology for in vitro digestibility estimation of protein concentrates from Azorean macroalgae and its amino acid profiles

The digestibility of a food protein may be obtained by using animal experiments but this is an expensive and time consuming procedure. Digestion of macroalgae proteins by proteolytic enzymes has been reported [1]. However, in these studies the in vitro protein digestibility was only based on single enzyme digestion. Multi-proteolytic enzyme system, which are more similar to the actual digestion environment in vivo have a good approximation of the true protein digestibility [2]. The objective of this study was to provide an estimation of protein digestibility of the Azorean macroalgae (AM) Ulva rigida, Fucus spiralis and Porphyra sp. using a multienzyme system and also to determine their amino acid profiles, in order to evaluate if these AM may be of nutritional value and have some impact on human health. The in vitro digestibility was determined in the protein concentrate (PC) suspension, extracted by the method described by Wong and Cheung [2]. The starting pH (8.00) of the mixture PC plus multi-enzymes (freshly prepared) at 37 °C changed and was exactly measured after 10 min. The results show the values of 81.40%, 84.31% and 85.07% for Porphyra sp., U. rigida and F. spiralis, respectively, expressed as a relative percentage of that of the sodium caseinate normalized at 100% (Fig. 1). The amino acid profiles are important in evaluating the nutritive quality of proteins, the digestibility of that is the primary determinant of the availability of its amino acids. Table 1 shows the AM amino acids profiles which contain all of the essential amino acids (EAA). The EAA percentage of the total amino acids were 55.23%, 56.73% and 63.50% for U. rigida, Porphyra sp. and F. spiralis, respectively, showing that AM have higher EAA content than casein (43.60%), leguminous plants (45.40%) and ovalbumin (52.40%). In conclusion, the in vitro protein digestibility, although not as accurate as the in vivo method can be completed within 1 hour with a high degree of estimation.

Fig. 1: Relative percentage of Azorean macroalgae protein digestibility to sodium caseinate normalized at 100%.

Tab. 1: Amino acid profiles of Azorean macroalgae (mg/g of protein).

Amino Acid (AA)	Porphyra sp.	Fucus spiralis	Ulva rigida
Aspartic acid	13.73 ± 0.25	5.52 ± 3.09	5.63 ± 0.07
Glutamic acid	10.30 ± 0.15	12.12 ± 0.10	7.63 ± 0.08
Serine	5.55 ± 0.13	11.47 ± 0.12	3.27 ± 0.03
Glycine	7.19 ± 0.07	7.45 ± 0.05	4.40 ± 0.04
Histidine*	2.33 ± 0.05	3.20 ± 0.03	-
Arginine*	5.93 ± 0.05	11.72 ± 010	2.99 ± 0.02
Threonine*	11.21 ± 0.10	10.85 ± 0.09	3.04 ± 0.04
Alanine	3.17 ± 0.02	4.06 ± 0.05	1.27 ± 0.04
Proline	6.12 ± 0.04	6.90 ± 0.07	2.32 ± 0.06
Tyrosine	5.27 ± 0.06	7.78 ± 0.08	6.28 ± 0.09
Valine*	7.15 ± 0.04	11.14 ± 0.12	2.74 ± 0.04
Methionine*	2.05 ± 0.05	6.36 ± 0.06	1.43 ± 0.04
Leucine*	18.45 ± 0.27	15.46 ± 0.19	14.51 ± 0.11
Isoleucine*	8.20 ± 0.11	15.31 ± 0.20
Phenylalanine*	3.73 ± 0.02	9.82 ± 0.08	1.78 ± 0.03
Lysine*	8.26 ± 0.12	12.54 ± 0.12	2.38 ± 0.04
Triptofan*	nd	nd	nd
EAA (%)	56.73	63.50	55.23
Values are mean ± SD (n = 3). * Essential amino acids (EAA), nd – not detected.

Keywords: macroalgae, proteolytic enzymes, amino acids, protein digestibility

References:

[1] Fleurence J, Lecoeur C, Mabeau S, Maurice M, Landrein A. Comparison of different extractive procedures for proteins from the edible seaweeds ulva-rigida and ulva-rotundata. J Appl Phyc 1995; 7: 577 – 582

[2] Wong, KH, Cheung PCK. Nutritional evaluation of some subtropical red and green seaweeds Part II.In vitro protein digestibility and amino acid profiles of protein concentrates. Food Chem 2001; 72: 11 – 17