The Role of Peracetic Acid in Bloodmeal Decoloring

Abstract

Hydrogen peroxide (HP) can degrade soluble heme, forming yellow or colorless degradation products. Thermal treatment during bloodmeal production changes the conformation of oxyhemoglobin trapping heme in hydrophobic protein regions or forms methemoglobin (metHb) heme which catalytically removes HP. As a result, HP can only degrade a portion of the heme present in bloodmeal leading to poor decoloring. Equilibrium peracetic acid (PAA) solutions can effectively decolor bloodmeal. This work assessed the ability of PAA to decolor bloodmeal and the mechanism by which it occurs. The inability of HP to decolor bloodmeal is determined by the fact that it is unable to permanently degrade metHb heme, or hydrophobically trapped heme. Addition of organic acids to HP led to significant swelling of the protein chains but also to poorer decoloring and lower HP consumption compared to PAA. This suggested that in the case of PAA solutions, where bleaching was facile, the reason PAA solutions are capable of decoloring bloodmeal was due to the action of the PAA molecule against heme, whereas HP and acetic (ethanoic) acid played only minor roles in total bleaching. The decolored protein powder has reduced odor and whiter color, and is suitable for applications such as bioplastics.

Changes to amino acid composition of bloodmeal after chemical oxidation

“…46 The destruction of the ferric haem species results in an overall loss of iron ( Figure 2) as free ferric ions are highly soluble in an acidic environment and are subsequently lost during the neutralisation and filtering stages of decolouring. 10 Acetic acid increased iron solubility and is often used to strip iron from solubilised haemin during the preparation of protoporphyin from red blood cells, 47 despite lower HP consumption and an accompanying lower decolouring efficacy. At least 3 wt% PAA is required for adequate decolouring, and improved haem degradation is evidenced from a significant loss of iron.…”

“…Using 1 -2 wt% PAA resulted in minimal decolouring, 10 most likely due to insufficient degradation of the haem species present, accompanied by minimal loss of iron (Figure 2). 10 Both PAA and HP are strong oxidants known to form various reactive oxygen and free radical species. At 5 wt% PAA a gel-like mixture formed, trapping free iron, which can be removed by washing with distilled water to give an iron content of 1.04 mg/g BM.…”

“…2 Peracetic acid, which is an equilibrium mixture of peracetic acid, hydrogen peroxide and acetic acid, has been used extensively since the early 1940s due to growing concerns over the environmental impact of chlorine. 3,10 However, peracetic acid adequately removed the colour from bloodmeal, with each component of the PAA solution performing a specific function in the overall decolouring and deodorising mechanisms. It does not form harmful disinfection by-products and decomposes safely when discharged into the environment.…”

“…It is used as a bleaching agent for textiles, as a disinfectant, [4][5][6][7] as well as in wastewater treatment. 10 The presence of several reactive species and the formation of free radicals, resulted in oxidative damage to the proteins as the radicals underwent auto-reduction reactions. 8,9 Common oxidants such as hydrogen peroxide are unable to degrade all of the haem present in bloodmeal due to the various oxidation states of haem-iron in haemoglobin.…”

“…13 However, a later study indicated that performic acid also degraded serine, threonine, tyrosine, phenylalanine and histidine, while PAA oxidation resulted in the conversion of all cystine to cysteic acid, with only small losses of tyrosine, phenylalanine and histidine. 10 Helices, sheets, turns and coils which define the secondary structure of the protein are modified by oxidation. As a result, oxidation of hair and wool by hydrogen peroxide or peracetic acid led to a loss in tensile strength proportional to the number of cystine residues degraded.…”