Protein Oxidation 101: 8 Simple Rules to Minimize PROTOX and Maximize the Proven Benefits of High(er) Protein Diets
|You're not going to like it, but not all of the protein foods in this photo deserve the attribute "SuppVersity Suggested"|
For those of you who are now wondering PROTOX is / are and why they are (literally) a matter of life or death, I suggest you go back to my previous article about the (ill) health effects of oxidized dietary (!) proteins from Thursday, May 19, 2016 (read the article | as always, for free!).
In view of the fact that this article got longer than the average "101" article, I'd suggest that anyone who is in a hurry fast forward to the list of eight simple rules I announced in the title of this article. You can bookmark the rest for later, print it to read it in bed or simply rely on my interpretation of the implications of what we know about the various ways processing and storage can damage proteins :
- Cooking, frying, baking, i.e. heat treatment(s), in general - While you don't have to eat your meat, fish and dairy raw, those of you who "fry their proteins to death" and eat their steak well-done are at a higher risk of exposing themselves to exuberant amounts of oxidized proteins than the rare steak conconnoisseurs.
While the number of studies testing for protein oxidation in meats during cooking is higher than those on any other protein source, their number is, compared to the one of studies investigating the oxidation of fats and cholesterol in meat products, still low and their significance is crippled by the use of either inappropriate markers of protein oxidation or different markers that make it virtually impossible to compare the results of one study to another.
An example of the initially mentioned problem, i.e. the use of inappropriate markers of protein oxidation, would be the 1997 study on the effects of different cooking methods on some lipid and protein components of hamburgers by Rodriguez-Estrada, M. T., et al. (1997). Their use of free form amino acids as marker of protein oxidation suffers from the presence of the latter in raw meat and their drip loss during cooking.
Figure 1: In contrast to the amount of free amino acids, the formation of Schiff bases provides reliable information about the oxidation of protein during e.g. cooking (data from Gatellier. 2010).
Furthermore, Gatellier's and other studies indicate that the formation of protein oxides which starts at relatively low temperatures of only >65°C does not begin to really take off before temperatures of 123-207°C - temperatures as you would see them if you fry your foods and can be reduced (albeit not significantly | 1300% increase vs 3500% increase | cf. Figure 2) if the cattle has been fed anti-oxidant rich diets.
Figure 2: Effect of diet and cooking parameters on protein oxidative modifications (Gatellier. 2010).
You must not forget, however, that the data in Figure 1 also shows that even the quality L+R meat is not fully protected from oxidation when it is heated at high(er) temperatures for more than 60 seconds - and that's something that is going to happen even for the most bloody (non-raw) steak. "t "and "T", i.e. time and temperature, are thus not the only, but the most significant determinants of protein oxidative modifications (cf. Figure 3).
An increased drip loss suggest increased protein oxidation: It's not just annoying if your meat weights only half of what it weighed before cooking, it is also an albeit not 100% reliable indicator or, I should say, correlate of increased protein oxidation. That's at least what a 2012 study by Traore et al. indicates: in said study, the researchers analyzed the effects of heat treatments on meat from the M. longissimus thoracis from Galia and Redone pigs. What they found was a striking and statistically significant correlation between the presence and level of oxidized proteins and the drip loss during cooking / frying. This observation does not only suggesting a possibly reduced ability of oxidized proteins to retain water, but also the possibility of using the drip loss, which is a marker of meat quality, anyways, as an easily accessible indicator / estimate for protein oxidation.
Figure 3: Time matters, but heat, too - Markers of protein oxidation in meat exposed to 100°C (grey) and 270°C for the time in minutes indicated on the x-axes (Santé-Lhoutellier. 2008).
When the time of exposure is short, the corresponding +200% increase in carbonyls (a marker of PROTOX | see Figure 3) that occurs at low temperatures is allegedly relatively small. If you are into slow-cooking your meats at "low" temperatures for several minutes, any low temp. advantage would be lost, though.
- Traditional processing methods to increase the storage time like dry-curing or fermentation - In contrast to the effects of heat treatment(s), the ones of other common processing methods are comparably under-researched. What we do know, however, is that dry-curing meats (and probably dry-aging, too - although a study on that has still to be done, to answer your Facebook question honestly, Matthew) can lead to sign. hydrolytic degradation of proteins (Toldrá, 1998). Furthermore, recent studies indicate that meat proteins will also undergo different, often more intense (compared to proteolysis) oxidative reactions during dry curing (Estévez. 2011).
Figure 4: Carbonyl content (nmoles/mg protein) in longissimus dorsi (unprocessed) and dry-cured loins from different pigs on diefferent diets; % indicates relative increase in protein oxidation (Ventanas. 2006).
|Steaming uses temps >60°C where proteins start to oxidize and steaming takes its time. It is thus not per se safe.|
- The hams, which are subjected to longer and more severe drying conditions, were found to have considerably larger amounts of protein carbonyls than the loins (≈ 9 nmol/mg protein vs. ≈ 1.3 nmol/mg protein). The manufacture of dry-cured meats involves a lengthy process (up to 36 months for Iberian dry-cured hams) and several operations such as salting, post-salting, drying and cellar (Ventanas. 2007). Little is known about the impact of each step on the onset and intensity of the oxidative reactions affecting to meat proteins. What studies have shown, however, is that ..
"[s]alting, which is a common operation for the manufacture of numerous meat products, may have an impact on protein carbonylation. The addition of sodium chloride has an impact on the ionic strength of the environment which in turn, affects the degree of assembly of MP (Wick, 1999) their exposure to pro-oxidants and hence, their susceptibility to carbonylation (Montero, Giménez, Pérez-Mateos, & Gómez-Guillén, 2005). In addition, several authors have proposed that NaCl could enhance the activity of Fe3+ or that Cl− derived from NaCl would improve the solubility of such ion, hence, stimulating their pro-oxidant effects (Kanner et al., 1991 and Osinchak et al., 1992)" (Estévez. 2011).Accordingly, you can assume that the protein oxidation increases with the amount of salt that's used when meat or, as the study by Osinchak et al. shows, fish is cured - an interesting observation that should remind you of the link between high salt intakes and heart disease, of which said link suggests that it could at least partly be mediated by the effect of salt on protein oxidation in processed meats and other high protein foods.
- Storage, cooling, freezing, high pressure and irradiation to reduce bacterial contamination, and packaging - You already know that cooked protein products have increased carbonyl levels compared to raw samples (1–3 nmol/mg protein in raw vs. 5 nmol/mg protein in cooked products), but the heat exposure is not the only threat to the proteins' integrity: cutting, mincing, and all the other processing steps protein foods undergo will likewise make significant contributions to the formation of protein carbonyls and other processes of protein oxidation.
Figure 5: Evolution of protein oxidation in liver pâtés from Iberian and white pigs (note the difference that exists even before storage) under refrigerated storage (Estévez & Cava. 2004). Figure 6: Changes in carbonyl content in chicken (a) leg meat and (b) breast meat as affected by freezing temperature and 6 months of storage at different freezing temperatures (Soyer. 2010). Figure 7: Effect of Storage Time (12 Days) on Nonirradiated and Irradiated Raw Chicken Breast Meats Stored at 5 °C on Carbonyl Content as Lipid (in µmol Acetophenone/10 g Meat | Rababah. 2004)
|Make no mistake: Eggs are healthy!.|
- Due to the large variability of the data reported by different authors for the amount of protein carbonyls in similar meat samples analyzed, it is unfortunately not possible to infer general patterns (Estévez. 2011) - that's also because the "extent of protein carbonylation is highly dependent on the origin of the meat, type of muscle, species and the storage [and feeding] conditions" (Estévez. 2011).
Another thing that appears to be proven is the fact that beef is significantly susceptible to protein carbonylation than pork - a fact scientists ascribe to the noticeably larger amounts of iron and myoglobin in cattle muscles (Lund. 2007a,b). Accordingly, it can hardly surprise you that a similarly lower propensity for protein oxidation has been found by Mercier et al. (1998) when they compared beef and turkey meat.
Figure 8: Determinants of the susceptibility of meat(s) and poultry to protein oxidation.
The same goes for the commonly used modified atmosphere packaging (MAP), which has been shown to contribute to increased myosin cross-links, and increased protein carbonyls especially if the "modified atmosphere" is high in oxygen (70% to 80% | Lund 2007a,b) - a condition that has been shown to reduce the formation of thiol groups, i.e. fat oxidation, but has the obvious downside of increasing protein oxidation. Alternative packaging methods would be available, 100% nitrogen (results are mixed, e.g. Zanardi. 2002; Leygonie. 2011) or vacuum-packaging (effectively reduced protein oxidation during storage compared to MAP | Lagerstedt. 2011), for example, but just like the use of additives and ingredients with proven antioxidant capacity they are rarely used and more research is necessary to determine which of them offers the best protection to both proteins and fat.
- None-meat, -poultry or -fish proteins react similarly - While there's lots of research on protein oxidation in meats, studies on other food sources are scarce, but show similar trends with respect to processing-induced protein oxidation.
In cheeses, for example, the lowest amounts of protein oxidation are found in "unripe" raw milk cheeses or cheese that was produced from milk that was semi-cooked or pasteurized at low (vs. high as in UHT milk) temperatures (Fedele. 2001).
Figure 10: Protein-bound carbonyls (PC) in selected cheeses from differently processed milk, i.e. unheated, semi-cooked and cooked milk as a raw ingredient (Fedele. 2001).
As the data in Figure 11 goes to show you, it takes only a few hours under a 15W UV lamp and/or a similarly "weak" fluorescent lamp to trigger rapid increases in protein oxidation in "milk", or rather what Scheidegger, et al. call milk, i.e. a liquid that was produced from water with commercially processed spray-dried whole milk powder, of which you can already expect that it has sign. higher baseline PC levels than regular milk.
To deliver milk in regular, opaque tetra packs instead of the hipster glass bottles is thus a very good idea! Much in contrast to the use of regular or hypoallergic milk powders in processed and baby foods, the consumption of sweet condensed milk or its unsweetened alternative, evaporated milk.
Table 1: Lysine damage in commercial milk samples (Mauron. 1990).
Corresponding data for vegetable proteins is unfortunately not available. Even though vegetable proteins usually don't come with high amounts of easily oxidizable lysine (casein has a 2.0 ratio of lysine to arginine, soy's ratio is 0.9 | Kritchevsky. 1979), iron and myoglobin, soy, pea, hemp, bean and other vegan / vegetarian protein sources are not immune to processing, i.e. heat-, light-, and pressure-induced protein oxidation or the ongoing deterioration of their protein structure during storage. Whether these effects are strong enough to turn an originally antioxidant or neutral food protein into a pro-oxidant dietary ingredient, will yet need further clarification in realistic scenarios. Initial evidence that this could be the case comes from a 2015 study by Chen et al. who administered heat-oxidized soy protein to broiler chickens and observed that it would impair the chickens growth performance - probably as a result of negative effects on the digestive function.
|Don't be a fool: There's no evidence that protein powders are "adulterated" with exorbitant amounts of protein oxidation products; and, even more importantly, the currently available evidence in favor of the beneficial health effects of whey and co. clearly refute the practical health significance of the most likely existing amounts of protein oxidation products in the average protein powder.|
What I have found out, though, is that whey proteins, like any other protein food, undergo heat-induced protein damage. For whey protein concentrates, Rector et al. report a rapid degradation of protein complexes when the protein is stored above the critical 60-65°C margin (Rector et al. used 80°C). Storage at 25°C for 1 year, on the other hand, resulted in polymerization of "only" 18% of the monomeric beta-lactoglobolins, and did not involve the formation of intermolecular cross-links, a characteristic feature of protein oxidation (Morr. 1993).
Whether the amount of protein oxidation products that certainly exist in casein, whey, soy, pea, and other protein powders is health-relevant, is therefore highly questionable. Furthermore, the well- and widely-established antioxidant effects of whey, which include, among other things, a reduction of protein oxidation in vivo (e.g. Haraguchi. 2011), would suggest that that the average whey protein doesn't just compensate, but over-compensate any potentially pro-oxidative effects of existing protein oxides by the anti-oxidant effects of its various antioxidant proteins and peptides (Tong. 2000; Peña‐Ramos. 2004; Peng. 2009).
In this context it may also be worth mentioning that a study by Fenaille et al. (2006), which investigated the protein-carbonyl (PC) levels in infant protein powder formulas, and is thus the study that comes closest to an analysis of PC levels in commercially available protein powders, found the amount of oxidized proteins to be not much different from those in unprocessed, cold-stored meat products. If certain quality standards during the production are met, it is thus unlikely that any potential worries you may have that protein powders could be much unhealthier than meat or other protein sources are warranted.
Figure 11: Influence of freeze–thaw cycles on TBARS (fat) & carnonyl (protein oxid.) in pork (Xia. 2009)
- avoid irradiated and or high pressure treated, industrially processed meats and prefer vacuum packaged meats over meats in modified atmosphere packaging w/ extra high oxygen levels (nitrogen is no problem) - the less processed and messed up the meat you buy, the less significant any further increases in protein oxidation you may induce at home will be; you should also ask your butcher if he already froze and thawed the allegedly "fresh" meat he offers - you may not believe it, but much of the "fresh" meat has actually been refrigerated and thawed at least once - especially, the more exotic cuts; also, vacuum packaging your meats at home makes as much sense as any other way of repackaging it to keep them fresh - none of them is going to be worse than simply putting the meat into the fridge in nothing but a simple plastic bag; pressure cooking is, as discussed previously probably not an issue (due to the comparatively low pressure), but the time your meats and other protein sources spend in the pressure cooker at relatively high temperatures could be
- use culinary herbs and spices - even though there is no data for each and every culinary herb and spice, the data that exists shows sign. reductions in protein, fatty acid oxidation and the formation of advanced glycation end-products (AGEs) for cloves, ground
cinnamon, ground Jamaican allspice, apple pie spice, oregano, ground
pumpkin pie spice, marjoram, sage, thyme, gourmet Italian
tarragon, mint, rosemary, Italian
poultry seasoning, turmeric, curry powder, chili powder, basil, nutmet, ginger, parsley, black pepper, and rosemary (Dearlove. 2008; Haak. 2008);
Figure 12: Protein hydrazones (expressed as nmol hydrazones/mg protein) gain during refrigeration of cooked burger patties with added fruit extracts and quercetin (Ganhão. 2010).
- appreciate quality, non-cured meat - a high drip loss (meaning the weight of your meat is significantly reduce when you cook it) is a common marker of low meat quality and a correlate of high protein oxidation (Traore. 2012); the same goes for the loss of water that occurred way before you bought the meat during curing; and, yes, this means if there's a significant source of oxidized proteins in your diet, your beef jerky, bacon and other cured meats are the prime suspects - not only, but especially if they're also high in salt
- choose low(er) fat meats, poultry, fish, dairy and vegetable protein over iron- and myoglobin-laden red meats - it's not just the lower iron and myoglobin content of poultry and fish that makes them more resilient to protein oxidation, it is also their low(er) fat content, which reduces potential cross-reactions of oxidized fats with proteins; this does not mean that you cannot eat fatty cuts of red meat, at all, but there's more than just epidemiological evidence that the consumption of high amounts of processed and/or improperly stored or packaged red meat is problematic; not just, but also because of high levels of oxidized proteins
- prefer raw or pasteurized over ultra-high temperature processed (UHT) milk / dairy products - in contrast to what the scaremongering on the internet would suggest the short application of relatively low temperatures (72°C) during the pasteurization process does not induce significant damage to the protein-structure of dairy products; that's in contrast to UHT, which is done with at least 53°C higher temperatures and is notorious for its effects on the protein structure - an effect you will even taste and smell (Clare. 2005)
- go easy on the heat and keep the duration of any heat exposure short - "well-done" or "tar-black" are words you shouldn't be forced to use to describe your dietary protein sources; you also don't want to simmer your meats and other high protein foods at 100°C (or even >65°C) for hours or fool yourself to believe that steaming your fish at 100°C for 10 minutes was so much better (in terms of protein oxidation) than frying it for 2 minutes
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