Processed fruit smoothies could be more nutritious, new study

Consumer interest in health and wellbeing has led to a growth in the market for fruit and vegetable smoothies, many of which are rich in micronutrients called polyphenols. If this beverage is purchased at a store, it’s likely to have been pasteurised with heat or pressure to prevent harmful bacterial growth and extend shelf-life. Now, a preliminary study in ACS’s Journal of Agricultural and Food Chemistry reports that processing smoothies with high heat also provides another benefit — it could make polyphenols easier for the gut microbiome to absorb.

Previous research found that food processing techniques like canning and boiling peppers and artichokes may increase the amount of polyphenols metabolised by the gut microbiota, potentially improving the health benefits of these foods. But gaps exist in scientists’ knowledge around other food processing techniques. So, Iziar Ludwig and colleagues investigated how pasteurisation could affect polyphenol digestion in the gut microbiome.

The researchers first prepared a smoothie made up of Granny Smith apples, green celery, green chicory, peppermint and lemon. They split up the smoothie into three parts: one was not treated, and the others underwent either high-pressure or high-temperature pasteurisation. Then, the smoothie samples were added to successive solutions meant to mimic the three stages of digestion — oral, gastric and intestinal. Post-digestion pressure- and heat-pasteurised smoothie samples had higher amounts of polyphenolic compounds (21% and 44%, respectively) available for absorption than the untreated sample (17%). The researchers attribute these results to changes in the plants’ cell walls, such as softening or rupturing, induced by pasteurisation that could favour the release of polyphenols into the body.

Smoothies pasteurised with pressure (left image) or heat (right image) have higher amounts of digestible polyphenols than raw smoothies. Image credit: Iziar Ludwig

Finally, to analyse gut microbiome transformations of polyphenols, the digested samples went through a laboratory version of colonic fermentation in vials containing human faeces as the microbiota source. The gut microbiota converted most polyphenols into smaller derivatives, such as phenylpropanoic acids. Some of these derivatives have previously demonstrated antidiabetic, anti-inflammatory and chemopreventive effects. The researchers determined that the largest microbiota conversions happened in the high-temperature, post-digestion smoothie sample because it started fermentation with higher overall polyphenol levels.

The researchers said this work emphasises how smoothie processing could lead to new beverage products with enhanced bioaccessibility.

Image credit: iStock.com/t:fortyforks