YOGHURT UNHAIRING A missed opportunity?

Image created by Deep AI (deepai.org)

In December 1986 a group out of the now defunct Protein and Leather department (headed by Heidemann) in Darmstadt published a paper that received some attention - but did not manage to influence the industry to the extent it should have. The group was trying to develop a new preservation method using a technology that Germans have used for centuries – fermentation using Lactobacillus. Sauerkraut, pickled vegetables, and cheese have all benefited from the generation of acidity permitted by the bacteria generating lactic acid in anaerobic conditions to prevent food-spoiling bacteria from being able to grow.

Most food-spoiling bacteria are mesophilic, that is they like the “Goldilocks” growing conditions of the majority of bacteria – neutral pH, mammalian body temperature, and low ionic strength/toxicity. Lactic acid will change those conditions giving advantage to the Lactobacillus bacteria – an exclusive access to the nutrients in that environment. A similar environmental manipulation occurs with the manufacture of beer and wine. The changes to the environment are so profound that the Russian (now Ukrainian) immunologist, Élie Metchnikoff, proposed the leaky gut syndrome hypothesis – that the human colon was “leaky” and allowed bad bacteria into the body – remedied of course by the consumption of lactic bacteria. The hypothesis has some traction, and the modern probiotic, yoghurt, kefir, and fermented product industry holds this as its central tenet.

Preservation and accidental unhairing
The German research group wanted to use some of the acquired knowledge outlined above to be able to achieve hide and skin protection. The experiment was designed and executed with a culture of Lactobacillus that was inoculated onto the hides and the mixture was agitated every minute (per hour) for 36 hours. The effect was profound – 99% of the hair could be removed with pushing. Likewise, the keratinous epidermis, sloughed off often with the hair still incorporated into the hair follicle opening in the epidermis (a big hairy mat). To make the inoculum (prepared in advance), the bacterial inoculation was introduced into water (300%), sodium chloride (0.3-1.5%), and whey protein (33%). Nutrients for the bacteria included manganese sulfate (MnSO4.H2O) and potassium chloride, 0.02% and 0.2% respectively. To control the growth of yeasts and fungi, sorbic acid (probably through potassium sorbate) was added at 0.05% concentration. Of that stock culture between 1/10 and 1/50 was taken per hide.

Fresh hides were used after they had been green fleshed after a simple wash. The hides were covered in the inoculum and spent time agitated into the suspension. The stirring was kept to a minimum and the temperature of the fermentation was held between 28-32°C, with the pH between 3.8 and 4.4. A higher growth was experienced at the lower end of that temperature range.

Unhairing action
The unhairing action was a surprise to the team, who would have been content to show that the bacteria preserved the fresh hides and allowed them to be stored until they were required by the tannery. The hair removal was high, with fine hairs remaining that the research team further destroyed with a reliming (a high pH reliming – although the work does not make this explicit). This work was replicated in an attempt at LIRI in the late 90s through BSc (Hon) student work, but did not manage to achieve quite the same success as the work indicated in this research – so it may be that the pre-growth of the bacteria requires some skill and careful control in the fermentation process.
Is the work viable as an unhairing or preservation system? Is it worth doing in the tannery? Salt can be bought at between $60-120 per tonne. In other words, 6-12 c per kg, that makes it a very cheap chemical. Whey protein, on the other hand, is now a valued ingredient in health and fitness so it no longer commands the waste ingredient category and price. The point being that the preservation cost would make the method completely unviable. Other waste protein sources could change this, however.
Lactobacillus requires the lactose sugar to kick start its growth, together with the other proteins and fats present in the whey, the bacteria can reach great numbers. The bacteria, in their great number, can then start eating the proteoglycans in the hide and skin - and the paper presented evidence of how much those proteoglycans get degraded by the bacteria. The scientists looked for proteolytic (and especially collagenolytic) activity and found none, meaning the technology was safe for preservation. No theory was advanced for how the unhairing took place

Implications
The paper was not a revelation that there was a possible technology that has not been adopted. The publication advances the idea – with the expectation that young scientists should be curious enough to look at possibilities that arise from this kind of research. What are the limitations, what is the mechanism (or unknown chemical) that the lactic soup uses to cause hair release? What does the bacterial digestion of proteoglycan mean for the future of pickling operations?

The work has never been followed up, as far as literature searches can show. In the 1990s the research at LIRI (never published) posited the idea that the tanning process could be largely acid based. Currently the pH profile of the leather making is neutral/slightly alkaline for soaking; moving to high pH for liming unhairing; back to slightly alkaline for deliming/bating; low pH for pickling/tanning; slightly less acidic for fixation (basification); neutralised further for post-tanning; and back to slightly acidic for final fix. Even an expert could agree that there is a lot of pH jumping around.

The Lactobacillus work shows that at the very least the process could eliminate the alkaline stage – and the work at LIRI tried to show that the high pH part of the process could be eliminated in principle with the use of acid preservation, unhairing, enzyme treatment, and tannage. Since those times some of the chemical companies have introduced an acidic compatible post tannage that was not available back then. A largely acidic effluent, whilst making balancing more difficult, could mean that with lime treatment the treatment could be relatively easier.

Whichever way the tanning industry moves in the future, it is worthwhile taking a look at potential disruptions like this research offers and dreaming of a day where time-savings, fewer chemical steps, and innovations can be found.

In the next issue: The landscape of the last few years, in the area of post tanning and tanning has been plagued by some very high-profile restrictions being placed on chemistry used in the tannery (e.g., phenol, formaldehyde, bisphenol S, melamine, and others). The next article will look at what has been restricted and what is left for a tanner to use – and a sneak peek at what could be the obvious replacements.