Macadamia nut effects on cardiometabolic risk factors: a randomised trial

We sought to examine the effects of daily consumption of macadamia nuts on body weight and composition, plasma lipids and glycaemic parameters in a free-living environment in overweight and obese adults at elevated cardiometabolic risk. Utilising a randomised cross-over design, thirty-five adults with abdominal obesity consumed their usual diet plus macadamia nuts (~15 % of daily calories) for 8 weeks (intervention) and their usual diet without nuts for 8 weeks (control), with a 2-week washout. Body composition was determined by bioelectrical impedance; dietary intake was assessed with 24-h dietary recalls. Consumption of macadamia nuts led to increased total fat and MUFA intake while SFA intake was unaltered. With mixed model regression analysis, no significant changes in mean weight, BMI, waist circumference, percent body fat or glycaemic parameters, and non-significant reductions in plasma total cholesterol of 2⋅1 % (-4⋅3 mg/dl; 95 % CI -14⋅8, 6⋅1) and low-density lipoprotein (LDL-C) of 4 % (-4⋅7 mg/dl; 95 % CI -14⋅3, 4⋅8) were observed. Cholesterol-lowering effects were modified by adiposity: greater lipid lowering occurred in those with overweight v. obesity, and in those with less than the median percent body fat. Daily consumption of macadamia nuts does not lead to gains in weight or body fat under free-living conditions in overweight or obese adults; non-significant cholesterol lowering occurred without altering saturated fat intake of similar magnitude to cholesterol lowering seen with other nuts. Clinical Trial Registry Number and Website: NCT03801837 https://clinicaltrials.gov/ct2/show/NCT03801837?term = macadamia + nut&draw = 2&rank = 1.

Microbial Load and Prevalence of Escherichia coli and Salmonella spp. in Macadamia Nut Production Systems

ABSTRACT

This study evaluated the potential impact of environmental factors and harvesting practices on the microbial load of macadamia nuts. Three farms located in primary macadamia nut production regions, the Mbombela (A), Barberton (B) and White River (C) areas in Mpumalanga Province, South Africa, were sampled over a 2-year period. A total of 264 irrigation water (54), soil (30), and macadamia nut (180) samples were collected and evaluated for microbial load. All water samples had mean Escherichia coli loads below 1,000 MPN/100 mL, which is the standard regulatory requirement for agricultural water considered fit for irrigation in South Africa. Mean total aerobic plate counts of nut-in-husk on-tree samples (3.91 log CFU/g; n = 60) were higher after harvesting (5.98 log CFU/g; n = 60) but were lower after dehusking (to 4.89 log CFU/g; n = 60) on nut-in-shell samples. Salmonella spp. were only detected in water samples from farm B (67%; n = 18) and farm C (15%; n = 18). Neither Listeria monocytogenes nor Salmonella spp. were detected in the soil samples. E. coli was only detected in 20% (n = 10) of soil samples collected from two farms (farms A and B). None of the E. coli isolated in this study was positive for the eae, stx1, and stx2 enterohemorrhagic E. coli virulence genes. This study provides basic data that can be used in the development of macadamia nut-specific hazard assessment tools within primary production environments.

HIGHLIGHTS

Inactivation of Salmonella and Surrogate Bacteria on Cashews and Macadamia Nuts Exposed to Commercial Propylene Oxide Processing Conditions

Propylene oxide (PPO), a chemical fumigant, has been validated to reduce Salmonella on bulk almonds but has not been evaluated for other tree nuts. There is a need to identify nonpathogenic surrogate microorganisms whose inactivation is comparable to that of Salmonella to assure effective PPO processing parameters in different packaging configurations without introducing Salmonella into the pasteurization facility. The objective of this research was to compare the reduction of Salmonella and three potential surrogate bacterial strains, Enterococcus faecium ATCC 8459, Pediococcus acidilactici ATCC 8042, or Staphylococcus carnosus ATCC 51365, on cashews and macadamia nuts processed by using PPO. Whole cashews and macadamia nuts were coinoculated with a five-strain cocktail of Salmonella and one surrogate, dried to the original water activity of 0.44 to 0.51 before being packaged in woven polypropylene bags (2.3 kg), and shipped overnight in Styrofoam containers under ambient conditions to a commercial facility for PPO treatment. Salmonella and surrogates were recovered by vigorous shaking in phosphate buffer (1:1, m/v), serial diluted, and plated onto tryptic soy agar with an overlay of xylose lysine Tergitol 4 for Salmonella or mannitol salt agar or bile esculin azide agar for each surrogate. The mean log reductions of Salmonella and each surrogate ( n = 18), within a sample and among all trials (three independent), were compared by using a matched pairs t test. Reduction in log CFU per gram of Salmonella was significantly greater than that of E. faecium on both macadamia nuts (7.3 ± 0.19 versus 6.4 ± 0.31) and cashews (5.4 ± 0.15 versus 5.1 ± 0.25) and significantly greater than P. acidilactici on both nuts (7.8 ± 0.22 versus 6.3 ± 0.33 on macadamia nuts and 4.9 ± 0.22 versus 4.1 ± 0.25 on cashews). Reduction of S. carnosus exceeded that of Salmonella. E. faecium and P. acidilactici may be considered as surrogates for Salmonella on whole macadamia nuts and cashews processed by using PPO.