Food as medicine: Investigating antioxidant levels in homemade and commercial apple cider vinegar

Foods that are high in natural antioxidants can help protect against this oxidative stress.

Taichi Takeuchi, former Bachelor of Applied Science student at the Universal College of Learning (UCOL) explains, ‘Fruit and vegetables are the main source of dietary antioxidants, but when we ferment them first, we can increase their antioxidant levels even more – a great example of this is making vinegar from fruit.’

Takeuchi set about investigating one of the most common types of fruit vinegar – apple cider vinegar or ACV – to find out if commercial or homemade vinegar offers us the most protection. He was also curious about what gave ACV in general a relatively high level of antioxidants.

‘Usually, darker coloured fruits have higher concentrations of phenolic acid, which is what gives them their antioxidant properties. It’s usually the same with dark and light-coloured vinegars, but ACV is very pale, so it made me wonder what was causing the high level of antioxidants if it wasn’t phenolic acid. It was something that wasn’t in the literature,’ says Takeuchi.

In addition, Takeuchi wanted to determine whether their organic acid and/or sugar profile contributed to the antioxidant activity. He selected nine ACVs in total – including six commercial New Zealand-made ACVs, one well-known American brand, and two local, homemade ACVs for his research. He sourced the commercial ACVs from supermarkets and organic shops while the two homemade ACVs were donated. One homemade ACV was fermented for two months, while the other one was fermented for a year.

Takeuchi undertook his research over a two-month period in 2020. He used a process of ferric reducing antioxidant power (FRAP) assay and identified that the two homemade vinegars had significantly higher antioxidant activity than the commercial ACVs.

‘One of my results was very unexpected, I was surprised that the homemade ACV had such a high level of antioxidants but also a high level of sugars. Sugars usually have a negative impact on antioxidants,’ says Takeuchi.

He suspects that the discrepancy is most likely because homemade vinegar is fermented with naturally occurring yeast and microbes from the skins of apples which results in incomplete fermentation of sugars to alcohols. By contrast, commercial ACVs use standardised bacteria to make the fermentation process more efficient and uniform. Identifying which microbes are most effective at producing antioxidants is a potential topic for further research.

Takeuchi wanted to explore what was contributing to the higher antioxidant levels in the homemade vinegar. He identified and measured the levels of organic acids and sugars in each of the vinegar samples through a process called high-performance liquid chromatography (HPLC), which is used to analyse known chemical compounds, and nuclear magnetic resonance spectroscopy (NMR), which is used to analyse unknown compounds.

The two homemade vinegars contained higher levels of sugars than the commercial vinegars – this was true of all the three identified sugar types – glucose, fructose and lactose. The commercial vinegars were found to contain only small levels of fructose, and no glucose or lactose, probably due to more complete fermentation.

The organic acid composition was also different in the homemade vinegars. They contained malic acid, but this was not found in the commercial varieties. Oxalic acid was seven to 16 times higher in the homemade vinegars compared to the commercial varieties. Takeuchi proposes that the higher sugar content in the homemade samples may, in the presence of these organic acids, help maintain their antioxidant levels.

‘The findings from this research confirmed that homemade varieties of ACV may be healthier due to their higher level of antioxidants. These increased levels may be related to the natural fermentation process producing different sugar and organic acid profiles in contrast to the commercial varieties. The good news is that although commercial varieties have comparatively lower antioxidant levels than homemade options, they are still beneficial for combatting damage caused by oxidative stress,’ says Takeuchi.

Takeuchi is currently preparing his ACV research for publication in a food science journal.

• Taichi Takeuchi was a third year Bachelor of Applied Science student at the Universal College of Learning (UCOL) when he undertook this research as part of his course work. He is continuing his study at Massey University and taking a Graduate Certificate course in chemistry. He hopes to study at postgraduate level next year. Contact Taichi Takeuchi.
  
  
• Takeuchi’s research was supervised by Dr Dorota Starzak, a member of the UCOL Applied Science staff.
  
  
• Dr Wade Mace from AgResearch and Dr Patrick Edwards at Massey University provided additional assistance analysing some of the chemical compounds present in the vinegars.
  
  
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