Być może ujawnia się tu właśnie niedoskonałość ''zwierzęcego'' wyznaczania BV ... Poniżej więc zamieszczam dalsze fragmenty artykułu, nie wygląda to na dowcip czy luźne spekulacje, w skrócie: szczury, przy pomocy których wyznaczano BV białek (w latach czterdziestych ubiegłego wieku), posiadają o 50% (!) wyższe zapotrzebowanie na metioninę niż organizm człowieka, co z kolei wynika z faktu, iż keratyna tworząca sierść jest bogata w cysteinę, powstającą właśnie z metioniny... dlatego ich organizmy chłonęły whey'a jak gąbki..., co zostało później wykorzystane przez producentów odżywek...ale to już inna historia
Poniżej szczegóły z autorami badań, datami, itp.
Hair and feathers are made of the protein known as keratin, which is rich in the sulfur-containing amino acid, cysteine (found in keratin in its oxidized form, cystine).
Cysteine can be produced in animals from another sulfur-containing amino acid, methionine. Since whey has more sulfur-containing amino acids than casein, hair- or feather-covered animals require less whey than casein to achieve protein balance. But this advantage will clearly does not apply to humans, a relatively hairless and featherless species, as the Boirie et al. study would seem to agree.
Nevertheless, studies performed over a half-century ago on hair- or feather-covered animals which demonstrated the ‘superiority’ of whey over casein, have been used as marketing ‘support’ by companies selling whey protein supplements.
Back in 1947, Tomarelli and Bernhart demonstrated that feeding whey protein (hydrolyzed -lactalbumin, more specifically) to rats produced greater protein retention than did casein (e.g., Tomarelli and Bernhart, 1947). The rats required about 70% more casein nitrogen than whey nitrogen per day to maintain nitrogen balance. These results are consistent with a number of similar studies performed around this time. The trouble is that these studies, too, were performed on animals covered either in hair or feathers –rats, dogs, and chickens, for instance. Thus, these data are applicable to barnyard animals, but not to humans.
Methionine is an essential sulfur-containing amino acid. As I noted earlier, it can be used by your body to synthesize cysteine (as in the production of keratin). Rats, which were commonly used in early studies to determine the frequently-quoted “Biological Value” (BV) of various dietary proteins, have a methionine requirement that is around 50% greater than you or I (Sarwar et al., 1989). This contributes to the lower BV numbers reported for dietary proteins containing relatively less methionine when such proteins are fed to rats, as compared to humans (Bricker and Mitchell, 1947).
Johnson et al. (1946) relate: “In the case of the human experiments, then, it would be concluded that the methionine requirement is lower, and is not a limiting factor in the attainment of nitrogen excretion in these experiments, or that the requirement is met by the body protein breakdown plus any dietary protein….Since the addition of further methionine did not reduce the nitrogen excretion on the low protein diet, it can be concluded that no more methionine is required under these circumstances than that represented by the entire sulfur excretion, or 1.4 gm methionine per day for our average subject….the present experiments suggest that the human body is not limited in its ability to conserve nitrogen by the need to meet a methionine requirement.”
Oczywiście wszystko to nie oznacza dyskwalifikacji whey'a jako pełnowartościowego
białka, pokazana jest tylko pewna niedoskonałość metod badawczych...
Pozdrowienia
Longus
ambroziak
Longus
posiadają gęstą sierść - ma to jednak pierwszorzędne znaczenie we wchłanianiu aminokwasów zawierających jak najwięcej związków siarki, bedących podstawowym budulcem sierści. I tak palmę pierwszeństwa z najwyższym BV otrzymał whey... gdyż właśnie zwierzęce organizmy najszybciej i najlepiej wchłaniały serwatkę...
Goral
Ale dzieki, cos tam kapuje :)
BYK
Grasik
