Yellow kiwifruit may boost immune health: study

The potential benefits could be due to the range of vitamins, minerals, and phytochemicals present in gold kiwifruit (Actinidia chinensis​ 'Hort16A'; Tauranga, New Zealand), report researchers from the Horticulture and Food Research Institute of New Zealand and The Hopkirk Research Institute, AgResearch. "These results indicate that Zespri Gold kiwifruit can modulate an antigen-specific immune response and suggest that Zespri Gold Kiwifruit may represent a new type of functional food ingredient,"​ wrote the researchers in the journal Nutrition Research​. If the results can be repeated in humans, gold kiwifruit products could join the growing immune health market. Increase in immune-boosting ingredients is increasing, and is one of the leading drivers in worldwide functional beverage industry, according to Zenith International. The researchers set about testing their hypothesis that the Zespri Gold kiwifruit could boost the immune system by feeding female C57B1/6 mice either a puree or juice concentrate for 20 days, during which they were orally immunised with ovalbumin - a protein from egg white - combined with a suboptimal dose of cholera toxin. This combination stimulates a mild gut-associated immune response of the type involved in dealing with infections. Lead author Denise Hunter reports that consumption of the kiwifruit puree was associated with an enhanced response to ovalbumin. This was characterised by significant increases in total immunoglobulins and immunoglobulin G (IgG) levels, compared to mice fed a sugar control solution. No significant differences between the juice concentrate group and sugar controls were observed. "This report demonstrates that the Zespri Gold Kiwifruit puree enhances an adaptive immune response to an orally administered antigen in mice,"​ wrote Hunter. "Such a finding suggests that this product has the potential to be a functional food ingredient, particularly because the process used to produce the Zespri Gold Kiwifruit puree facilitates retention of nutrients, vitamins, heat-sensitive phytochemicals, water-soluble polysaccharides, and dietary fibre present in the whole fruit." ​ In attempting to identify the biologically active nutrients, the researchers note that the results suggested that the superior carotenoid content may be responsible. "It should be noted that not all carotenoids have the same effect and that the balance between all nutritional constituents can be important to maintain immune function,"​ they stated. Specifically, studies have reported that lutein and beta-carotene may stimulate the production of antibodies in mice in response to an immune system. On the other hand, the fibre content of the fruit may also play a role, suggested Hunter and co-workers, noting that prebiotic fibres have been reported to stimulate an immune response via the stimulation of specific bacteria groups in the colon. "Further work, including a human feeding trial, would be required to confirm the immune-enhancing effects of Zespri Gold Kiwifruit processed products,"​ they concluded. Previously, studies from the AUT University in Auckland have reported that kiwifruit have laxative effects and could help combat serious cases of constipation, while studies from the University of Oslo have reported that two to three kiwifruit a day significantly reduced blood clotting in human volunteers and could offer protection from strokes and deep vein thrombosis. The study was funded by the Zespri Group. Source: Nutrition Research​ (Elsevier) April 2008, Volume 28, Issue 4, Pages 251-257 "Feeding Zespri Gold Kiwifruit puree to mice enhances serum immunoglobulins specific for ovalbumin and stimulates ovalbumin-specific mesenteric lymph node cell proliferation in response to orally administered ovalbumin" ​Authors: D.C. Hunter, M. Denis, N.A. Parlane, B.M. Buddle, L.M. Stevenson, M.A. Skinner