Macadamia Nut Research Articles

The Cardioprotective Properties of Selected Nuts: Their Functional Ingredients and Molecular Mechanisms.

Nuts have been known as a nutritious food since ancient times and can be considered part of our original diet: they are one of the few foods that have been eaten in the same form for thousands of years. They consist of various dry fruits and seeds, with the most common species being almonds (Prunus dulcis), hazelnuts (Corylus avellana), cashews (cashew nuts, Anacardium occidentale), pistachios (Pistacia vera), walnuts (Italian nuts, Juglans regia), peanuts (Arachia hypogaca), Brazil nuts (Bartholletia excels), pecans (Corya illinoinensis), macadamia nuts (Macademia ternifolia) and pine nuts. Both in vitro and in vivo studies have found nuts to possess a range of bioactive compounds with cardioprotective properties, and hence, their consumption may play a role in preventing and treating cardiovascular diseases (CVDs). The present work reviews the current state of knowledge regarding the functional ingredients of various nuts (almonds, Brazil nuts, cashew nuts, hazelnuts, macadamia nuts, peanuts, pecan nuts, pine nuts, pistachios, and walnuts) and the molecular mechanisms of their cardioprotective action. The data indicate that almonds, walnuts and pistachios are the best nut sources of bioactive ingredients with cardioprotective properties.

Sorption of four antibiotics onto pristine biochar derived from macadamia nutshell

In this study, the sorption properties of ciprofloxacin, ofloxacin, sulfamethoxazole, and trimethoprim on biochar derived from macadamia nut shells were investigated. The raw biomass was pyrolyzed at 600 °C to create a highly porous material with a surface area of 392 m2 g−1. The produced biochar was found to be a valuable material for both environmental remediation and carbon sequestration due to its high carbon and oxygen content. The sorption properties of four antibiotics on the produced biochar were compared using Bayesian nonlinear regression based on second-order kinetics and the Langmuir model. The Bayesian estimation successfully compared the adsorption coefficients of the antibiotics, which can be directly visualized through graphical grammar using the probability density distribution. The results demonstrated the ability of macadamia nut shell biochar to remove antibiotics from water at neutral pH, and this material has the potential to be used for treating other emerging contaminants.

Determination of Essential Elements in Selected Nuts Produced in Kenya

Nuts, when eaten regularly, have been shown to reduce the risk of developing obesity, diabetes, and cardiovascular disease. They contain healthy fats such as monounsaturated fatty acids and are high in protein, vitamins, fiber, phenolics, phytosterols, and essential minerals. Essential minerals are important in preserving good health and body immunity against infections. They are categorized as macro minerals or micro minerals. This study intends to determine the essential elements present in macadamia nuts and peanuts and explain the importance of these nuts to human health and the intake suitable for consumption. The two nuts were collected in triplets from each study area and transported to the University of Nairobi, Department of Chemistry laboratory. The moisture content of the nuts was determined by the gravimetric method. The samples were then wet digested followed by determination of the essential elements using atomic absorption spectroscopy (AAS). Moisture content results were as follows: Macadamia nuts recorded an average moisture content of 15.68% while that of peanuts was 3.89%. The spectrum of correlation coefficients extends from +1 to 0.9036. The results indicated that macadamia nuts from Magumoni had the highest levels of Ca (15.25 ± 0.35 mg/kg), Na (10.99 ± 0.17 mg/kg), Fe (6.96 ± 0.18 mg/kg), Mn (0.465 ± 0.276 mg/kg) and Cu (1.01 ± 0.45 mg/kg). Peanuts from the Kangemi market had the highest levels of Mg (49.45 ± 4.71 mg/kg), K (46.95 ± 0.35 mg/kg), and Zn (0.49 ± 0.01 mg/kg). Mg was the most abundant essential element in both nut samples. Comparing the results with WHO/FAO permissible limits for essential elements in food, the concentration of Fe, Zn, and Cu were within the recommended limits. The levels of K, Na, Mn, Ca, and Mg were below the recommended limits by WHO

A Review of the Macadamia Nut Sector in Zimbabwe

The scope of macadamia nut (macadamia spp) as an alternative export crop in Zimbabwe has not been extensively explored. This study is a review of related literature from published and unpublished materials, press documents, websites, informal interviews with key informants along the macadamia value chain to explore the historical and current trends in macadamia nut production in Zimbabwe, policy framework, smallholder farmer’ contribution and the constraints that they are facing for informed policy making. Macadamia is an important lucrative crop in Zimbabwe, mainly used for income generation especially among smallholder producers and for the country’s export generation. It was established that Macadamia is a fully established crop whose production in Zimbabwe is not yet commensurate to the opportunities that exists in the global market. Smallholder macadamia farmers are constrained by high production costs, weak marketing systems, lack of access to export markets, poor research and development and limited support from government. Zimbabwe exports raw macadamia nut in shells resulting in short supply chain and a disparity which underscores a missed opportunity for higher revenue and value addition within the country. Research recommends targeted training, capitation of extension staff and establishments of a macadamia research station. Government is also recommended to ensure and enabling environment to facilitate private sector investment in macadamia value addition.

Biomass attachment and microbiota shifts during porcine faecal in vitro fermentation of almond and macadamia nuts differing in particle sizes.

Nuts are highly nutritious and good sources of dietary fibre, when consumed as part of a healthy human diet. Upon consumption, nut particles of various sizes containing lipids entrapped by the plant cell walls enter the large intestine where they are fermented by the resident microbiota. This study investigated the microbial community shifts during in vitro fermentation of almond and macadamia substrates, of two particle sizes including fine particles (F = 250-500 μm) and cell clusters (CC = 710-1000 μm). The aim was to determine how particle size and biomass attachment altered the microbiota. Over the 48 h fermentation duration, short chain fatty acid concentrations increased due to particle size rather than nut type (almond or macadamia). However, nut type did change microbial population dynamics by stimulating specific genera. Tyzzerella, p253418B5 gut group, Lachnospiraceae UCG001, Geotrichum, Enterococcus, Amnipila and Acetitomaculum genera were unique for almonds. For macadamia, three unique genera including Prevotellaceae UCG004, Candidatus Methanomethylophilus and Alistipes were noted. Distinct shifts in the attached microbial biomass were noted due to nut particle size. Bacterial attachment to nut particles was visualised in situ during fermentation, revealing a decrease in lipids and an increase in attached bacteria over time. This interaction may be a pre-requisite for lipid breakdown during nut particle disappearance. Overall, this study provides insights into how nut fermentation alters the gut microbiota and the possible role that gut microbes have in lipid degradation.

Morphological and physiological responses of 14 macadamia rootstocks to drought stress and a comprehensive evaluation of drought resistance

Planting macadamia in karst rocky desertification areas has significant ecological and economic benefits. However, the production of macadamia in karst area are facing serious drought challenges due to the poor water holding capacity of soil, and less and uneven precipitation resulting with the rising of temperature in the world. Selecting and breeding drought-resistant rootstocks is one of the main measures to solve this problem in macadamia nut production in karst area. In this study, the morphological and physiological performance of half-sib family offspring of 14 macadamia cultivars were investigated under severe drought conditions and their drought resistance was evaluated comprehensively in order to select the most suitable macadamia rootstocks. Results revealed that the leaves of all rootstocks were damaged after drought stress. Among the tested rootstocks, the leaves of QA5 were damaged the most severely, and the leaves of the whole plants were chlorotic, followed by C11, A4, and NY2, while the symptoms in leaves of O.C and H2 was less obvious after drought stress for 30 d. At the same time, the O.C and H2 had the lowest drought injury index (DII), which was 0.40, while the QA5 had the highest DII value (0.82). The physiological indices, including malonaldehyde (MDA), superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), soluble protein (SP), soluble sugar (SS), proline (Pro) and relative electrolyte leakage (REL) increased (Drought tolerance coefficient, DTC > 1) after drought stress, while relative water content of leaves (LRWC), chlorophyll (Chl), relative water content of roots (RRWC) and root activity (RA) decreased (DTC < 1) in all cultivars. Except SP, SS and Pro, there were significant differences in other indexes among different rootstocks. The 13 physiological indices were transformed into seven independent, comprehensive indices through principal component analysis (PCA), whose cumulative contribution ratio reached 82.905%. The 14 rootstocks were divided into 3 categories based on the comprehensive evaluation value (D). The O.C and H2 were clustered into the drought-tolerant group, whose D values were 0.743 and 0.669, respectively. The NY3, 333, 788, NY116, NY1, NY2 were belonged to the intermediate drought tolerance group, the D values were 0.530, 0.508, 0.497, 0.465, 0.457 and 0.441 respectively. Lastly, A16, A4, C11. GR1, 695 and QA5 were clustered into low drought tolerance group with the lowest D values of 0.396, 0.391, 0.360, 0.360, 0.355, 0.324, respectively. The result of stepwise regression analysis showed that MDA, POD, APX, SS, REL, RRWC and RA were the most significant physiological and biochemical indices that played a significant role in drought tolerance, and could be used as the primary evaluation and identification indicators of drought tolerance of macadamia. These results indicated that the drought-resistant rootstocks of macadamia could improve their drought resistance by stimulating the cluster root development, increasing antioxidant enzyme activity and raising the content of osmotic regulatory substances under drought stress. Our study not only provided alternative rootstocks for macadamia drought-resistant cultivation, but also provided the theoretical basis for the drought-resistant rootstock breeding of macadamia by expounding the physiological mechanism of drought-resistance.

Contribution of insect flower visitors on macadamia nut set, retention and yield in central Kenya

The aim of this study was to evaluate the contribution of insects that visit macadamia flowers to nut set, retention, nut-in-shell, and kernel yields. The study was conducted at the Macadamia Research Centre in Kandara, Murang'a County, in three flowering cycles (cropping), from August 2020 to May 2022. Nut set, retention, and yield were assessed by randomly selecting twelve trees that were in full bloom at the study orchard in each of the flowering cycles. On each of the twelve trees, four branches of the same size were selected and tagged for the study. The branches were about 1 to 1.5 metres high from the ground. On each branch, one raceme at the bud stage was randomly selected and one of the four treatments administered. The treatments were (i) bagged during the day with mesh nets, (ii) bagged at night, (iii) bagged throughout the flowering season, excluding all insects, and (iv) racemes were left unbagged, thus having unlimited flower visitation by insects. There were significant differences on nut-in-shell yield (mass) (P≤0.05) in flowers that were unbagged (68.23 ± 4.03), bagged at night (61.50 ± 3.51), bagged during the day (6.53 ± 1.05) and those that were bagged throughout (4.45 ± 0.95). Racemes that had flower visitors fully excluded resulted in low nut-in-shell production. The initial nut set, retention, and ultimately the nut-in-shell yields were significantly increased in flowers that were left unbagged, thus insects had unlimited access. Macadamia nut set, retention, and ultimate yield (nuts-in-shell and kernel) is largely dependent on the presence of insect flower visitors.

Lipid supplementation with macadamia by-product reduces methane emissions by sheep

Macadamia cake (MC) is a waste product from the macadamia nut industry with high nutritional value for animal nutrition. It has the potential to modify rumen fermentation, increase the efficiency of rumen microorganisms, and reduce methanogenesis. This study aimed to evaluate how the dietary lipid supplementation with MC modulates the methane (CH4) emission and nutrients digestibility of finishing lambs. Thirty-one lambs, approximately 90 days old and mean initial body weight of 26 ± 3.4 kg, were allocated to individual metabolic cages and subjected to in vivo digestibility assays for 24 days (17 days of adaption and 7 days of data collection). The four treatments included a Control group with no MC addition, and three groups with varying amounts of MC inclusion in the diet: 4.5%, 8.5%, and 14% on a dry matter basis. The ruminal content was collected individually at the last day of the digestibility assay 2 to 3 h after the morning feed, to measure pH, protozoan count, and short-chain fatty acids. The animals were then moved to semi-open respirometry chambers for the in vivo measurement of CH4 emission. A completely randomized design was used in the study assuming MC intake (MCI) as fixed effect and each animal as random effect. The variables were submitted to tests of normality and homoscedasticity. The data was submitted to analysis of variance at a 5% significance level using the F test (P < 0.05) and polynomial regression analysis. Pearson’s correlation coefficient test was also applied to all variables. Daily dry matter intake or apparent total tract digestibility parameters were not affected by MCI (P > 0.05), while ether extract and gross energy intake showed the widest range of values, from 0.01 to 0.09 (kg/day) and 9.3 to 22.5 (MJ/day), respectively, increasing (P > 0.05) according to MCI. In addition, total digestible nutrients increased linearly with MC supplementation (P = 0.037). MCI had a significant suppressive effect on enteric CH4 production from 21.9 to 8.6 (L/day) (P < 0.05) and protozoan count (P < 0.001) from 291875 to 69500 (n/mL), while a cubic (P = 0.03) and linear (P = 0.05) effect was observed for ammonia nitrogen and butyric acid, respectively. Macadamia cake may be used as an ingredient in sheep diets and its inclusion up to 14% has shown promise in reducing daily emissions of enteric CH4 without compromising nutrient digestibility and ruminal fermentation, in addition to contributing to reducing the environmental impact by avoiding the disposal of this industrial by-product.

Effects of Supplementary Pollination on Macadamia Nut Set, Retention and Yield in Murang’a County, Kenya

Macadamia is a promising prime dessert nut with the potential of alleviating poverty and enhancing food security in Kenya. Nut set and subsequent development of nuts to maturity is dependent on pollination which is mediated by animals, and honey bees are the dominant macadamia flower visitors. However, macadamia is pollen deficit as not all flowers set develop to mature nuts, thus supplemental pollination results to better nut yields. There is limited information in Kenya among the smallholder macadamia growers on the importance of supplementing pollination to enhance nut yields. This study was conducted at Kandara Macadamia Research Centre and in a smallholder macadamia farm located 15 km from the research centre, which was purposively selected from July 2021 to May 2023. Assessment of the influence of pollinators and supplementing pollination to nut set, retention and final yields was done. Honey bee, (Apis mellifera L.) colonies were also introduced at the Macadamia Research Centre to enhance pollination and mitigate deficits. Racemes were bagged to exclude pollinators, others left open to unlimited pollinator access while others received supplemental hand pollination. The results demonstrate that macadamia is pollen limited and pollination is highly reliant on insect pollinators. There were significant differences (p &amp;lt; 0.001) among the bagged (pollinator exclusion), open and hand pollinated racemes in both farms. The initial nut set and retention was increased significantly (21.54%) in hand pollinated racemes compared to those that were left to open pollination (unlimited pollinator visits) depicting pollination deficit in farm B. Introduction of supplementary honey bee colonies at the Kandara Macadamia Research Centre, resulted to higher nut set, retention, nut-in-shell and kernels. Macadamia growers are encouraged to introduce honey bee colonies in their farms to improve yields and also address pollination deficits.

In Vitro Assessment of the Bioaccessibility of Zn, Ca, Mg, and Se from Various Types of Nuts.

The bioaccessibility of zinc (Zn), calcium (Ca), magnesium (Mg), and selenium (Se) from various nuts (Brazil nuts, walnuts, peanuts, almonds, cashews, pecans, hazelnuts, macadamia nuts, and pistachios) was assessed using a simulated two-phase model of enzymatic digestion in vitro. The levels of Zn, Mg, and Ca were determined by atomic absorption spectrometry, and Se was measured by inductively coupled plasma-mass spectrometry. All tested nuts were good sources of Mg, and most, except macadamia nuts, were also good sources of Zn (the standard portion covers over 15% of NRV-R (UE) 1924/2006). Brazil nuts had the highest Se content. Almonds and Brazil nuts were rich in Ca. Se demonstrated the highest bioaccessibility from nuts (27.7% to 70.65%), whereas Ca exhibited the lowest bioaccessibility (below 9%). Pistachios had the highest Zn bioavailability, while cashews excelled in Mg bioaccessibility. Macadamia and pistachios were top for Ca bioaccessibility, and Brazil nuts for Se. Bioaccessibility is positively correlated with fat (for Zn: r = 0.23), carbohydrates (for Mg: 0.44; for Ca: 0.35), and sugar content (for Zn: r = 0.36; for Mg: 0.46; for Ca: 0.40).

Gymnandrosoma aurantianum (Lepidoptera: Tortricidae): Calling Rhythm and Effect of Age on Female Sex Pheromone Titer and Male Antennal Responses.

The macadamia nut borer, Gymnandrosoma aurantianum Lima (Lepidoptera: Tortricidae), is the main pest of Macadamia integrifolia Maiden & Betche (Proteales: Proteaceae) in Central America. Despite its importance, there is little information on its reproductive behavior. We studied the calling behavior and effect of age on female sex pheromone production and male antennal response to the pheromone. Calling behavior of G. aurantianum females occurred at the onset of scotophase, between 17:00 and 20:00h. The mean time spent calling was 64min. It was observed that 30% of the 50 females exhibited a calling posture characterized by extrusion of the pheromone gland from the tip of the abdomen and they spread their wings slightly. Female age had no influence on the sex pheromone production, while male antennal response increased with age and pheromone dosage. The information obtained in this work contributes to understanding the sexual behavior of G. aurantianum and thus to the creation of strategies to control this important pest in macadamia.

The utility of macadamia nut legumin Mac i 2 and its conformational epitopes in the diagnosis of macadamia nut allergy

The utility of macadamia nut legumin Mac i 2 and its conformational epitopes in the diagnosis of macadamia nut allergy

Chemical differences between brown centre and white macadamia kernels

Nuts are susceptible to many quality issues, including discoloration defects in kernels. These discolouration defects can affect their market value and result in significant economic losses to both growers and processors. In macadamia, this quality issue is called brown centres and has been related to storage at high temperatures and moisture concentrations. However, the chemical differences between brown centre and white macadamia kernels have not previously been studied. We aimed to determine the chemical differences between macadamia kernels with brown centre defects and kernels that were white and cream coloured. We used brown and white kernel samples from 20 commercially processed batches of macadamia. From each batch, we selected brown centre samples and compared their chemistry with white kernel samples from the same batch. We compared the moisture concentration, sugar concentration, nutrient concentration, fatty acid profile and peroxide value of brown centre defect and white kernel samples. Our results showed that brown centres had a higher moisture concentration compared with white kernel samples (5.16 % vs 2.91 %, respectively, P < 0.05). Reducing sugars of fructose (0.61 %) and glucose (0.53 %) concentrations were only detected in brown centre, although the sucrose concentration was not significantly different. Most nutrient concentrations were higher in brown centres compared with white kernels. Nitrogen concentration was significantly higher in brown centre than white centres (2.10 % vs 1.82 %, respectively, P < 0.05). Calcium concentration was also higher in brown centre than white macadamia kernels (608.44 mg/kg vs 419 mg/kg, respectively, P < 0.05). Our study suggests that high moisture concentrations in macadamia kernels could have triggered the hydrolysis of sucrose into reducing sugars (fructose and glucose). In addition, reducing sugars and proteins can react in the Maillard reaction to form brown colouration in nuts. This is the first study to comprehensively compare the nutritional composition of brown centres and white macadamia kernels. We recommend appropriate drying and storing of macadamia nuts to prevent sucrose degradation into reducing sugars and decrease the formation of brown centres through the Maillard reaction.

Investigation on cost-effective composites for CO2 adsorption from post-gasification residue and metal organic framework

Cost-effective CO2 adsorbents are gaining increasing attention as viable solutions for mitigating climate change. In this study, composites were synthesized by electrochemically combining the post-gasification residue of Macadamia nut shell with copper benzene-1,3,5-tricarboxylate (CuBTC). Among the different composites synthesized, the ratio of 1:1 between biochar and CuBTC (B 1:1) demonstrated the highest CO2 adsorption capacity. Under controlled laboratory conditions (0°C, 1 bar, without the influence of ambient moisture or CO2 diffusion limitations), B 1:1 achieved a CO2 adsorption capacity of 9.8 mmol/g, while under industrial-like conditions (25°C, 1 bar, taking into account the impact of ambient moisture and CO2 diffusion limitations within a bed of adsorbent), it reached 6.2 mmol/g. These values surpassed those reported for various advanced CO2 adsorbents investigated in previous studies. The superior performance of the B 1:1 composite can be attributed to the optimization of the number of active sites, porosity, and the preservation of the full physical and chemical surface properties of both parent materials. Furthermore, the composite exhibited a notable CO2/N2 selectivity and improved stability under moisture conditions. These favorable characteristics make B 1:1 a promising candidate for industrial applications.

Identifying the optimal phenological period for discriminating subtropical fruit tree crops using multi-temporal Sentinel-2 data and Google Earth Engine

The accurate and appropriate monitoring of the spatial distribution of fruit tree crops is crucial for crop management and yield forecasting. Owing to both inter- and intra-farm fragmentation and overlapping phenological cycles, the classification of fruit tree crops in subtropical agriculture using single-date images is challenging. Therefore, this research aimed to identify the optimal temporal window in which the crucial phenological stages can be used to classify fruit tree crops in Levubu, Limpopo province, using a random forest (RF) classifier. Phenological metrics were extracted from 12-month Multispectral Instrument (MSI) images from Sentinel-2 (S2). The RF classification algorithm attained an overall accuracy of 84.89% and a kappa coefficient of 83%. The user accuracy ranged from 62 to 100%, while the producer accuracy ranged from 60 to 100%. An analysis of variance was used to assess whether the overall accuracies among the S2 monthly composites were statistically significant. The results showed distinct spectral differences between fruit trees. In April, there were differences observed during the harvesting and senescence of the mango and macadamia nut crops. In May, there were differences observed during the senescence of the macadamia nut, mango, and guava crops. In June and July, there were distinct spectral differences during the peak flowering stage of the avocado, macadamia nut, and mango crops, as well as in the fruiting stage of the banana crops. Followed by the red-edge bands, the shortwave infrared bands were significant in differentiating between the respective fruit tree crops. The results of this research provide evidence-based information that can assist farm managers and horticulturists in making informed decisions. This is critical in achieving effective agricultural management and in ensuring the sustainability of local horticultural systems.

Exploring the Prospects of Macadamia Nutshells for Bio-Synthetic Polymer Composites: A Review.

The global production of macadamia nuts has witnessed a significant increase, resulting in the accumulation of large quantities of discarded nutshells. These nutshells possess the properties of remarkable hardness and toughness, which are comparable to those of aluminum. Incorporating natural fillers to enhance the properties of composite materials for various applications, including light duty, structural, and semi-structural purposes, is a common practice. Given their inherent hardness and toughness, macadamia nutshells present an intriguing choice as fillers, provided that the manufacturing conditions are economically viable. With the urgent need to shift toward natural fillers and reduce reliance on synthetics, exploring macadamia nutshells as components of natural fiber composites becomes imperative. This review aims to comprehensively examine the existing body of knowledge on macadamia nutshells and their bio-synthetic polymer composites, highlighting key research findings, achievements, and identifying knowledge gaps. Furthermore, the article will outline prospective areas of focus for future research endeavors in this domain, aligning with the universal goal of minimizing synthetic materials.

Effect of Preharvest Ethephon Application on Selected Biochemical Components and Polyphenol Oxidase Activity in Macadamia Nuts

Ethephon is a plant growth regulator that triggers diverse responses in plants, such as fruit ripening, leaf senescence, hull senescence, stem elongation, and nut abscission. This study examined how the preharvest application of ethephon 480 SL® affects selected biochemical components and polyphenol oxidase (PPO) activity in two macadamia nut cultivars: ‘788’ and ‘Beaumont’. Ethephon was applied to the trees via a Cima mist blower at rates of 13.33 mL/L per hectare for the ‘788’ cultivar and 16.67 mL/L per hectare for the ‘Beaumont’. Following harvest, the nuts were stored at 25 °C for 72 days, and samples were taken at 18-day intervals. Standard procedures were used to assess the following: total phenolics, total flavonoids, 2,2,-diphenyl-1-picrylhydrazyl (DPPH) assay, Ferric reducing ability power (FRAP) assay, sucrose, total protein, and PPO activities. This evaluation was carried out across a total of four treatments: ethephon-treated nuts from the orchard floor (ED), ethephon-treated nuts from the tree (ET), untreated nuts from the orchard floor (CD), and untreated nuts from the tree (CT). The evaluation’s outcomes were analyzed using a principal component analysis (PCA), a correlation matrix heat map (CMHM), and a graphical assessment. The results unveiled significant correlations and associations among the assessed parameters. The correlation matrix heat map analysis highlighted a strong positive correlation (0.97) between the sucrose and the PPO activity in the ‘Beaumont’ cultivar, supported by the PCA analysis identifying the ED treatment as the most influential. At the storage period’s conclusion, the ED treatment had the highest sucrose content (18.63 mg/g) and polyphenol oxidase activity (1.06 U g−1). In the ‘788’ cultivar, a close relationship emerged between the phenolic content, the PPO activity, and the Ferric reducing antioxidant power (FRAP)’s antioxidant activity. Consistently, the CT treatment (untreated nuts) demonstrated positive correlations with several key parameters in both cultivars, displaying heightened phenolic content and antioxidant activities. Consequently, our findings indicate that the CT treatment, involving tree-harvested nuts without ethephon application, could be the preferred option for sustaining macadamia nuts’ quality and shelf life compared to other methods. Moreover, our study underscores the significance of proper storage conditions for maintaining the desired biochemical parameters of macadamia nuts. By comprehending the effects of distinct treatments and harvesting techniques, producers and processors can devise strategies to optimize storage conditions and uphold macadamia nut quality.

Prospects for Biological Control of Macadamia Felted Coccid in Hawaii with Metaphycus macadamiae Polaszek & Noyes, a New Encyrtid Wasp Native to New South Wales, Australia.

Macadamia felted coccid (MFC), Acanthococcus ironsidei (Williams) (Hemiptera: Eriococcidae), was first discovered in 2005 on the Island of Hawaii. Host plants are restricted to Macadamia species, with Macadamia integrifolia Maiden & Betche (Proteaceae) being grown in Hawaii for nut production. Approximately 6839 hectares macadamia nuts are harvested in Hawaii with an estimated farm value of USD 48.8 million (2019-2020 records). Exploration in Australia started in November 2013 for the evaluation of potential parasitoids being host specific for introduction into Hawaii. A dominant solitary endoparasitoid of MFC from New South Wales was discovered and described as Metaphycus macadamiae Polaszek & Noyes sp. n (Hymenoptera: Encyrtidae: Encyrtinae). Biology and host specificity testing were conducted at the Hawaii Department of Agriculture, Insect Containment Facility, on nine hemipteran and three lepidopteran eggs. Results indicated that M. macadamiae is host specific to MFC. There has been no evidence of parasitism or host feeding on any of the non-target insect hosts that were tested. Parasitoid emergence from the control (MFC) averaged 30.2% compared to 0% on non-target hosts. A low rate of parasitoid emergence in the laboratory (average 30.2%) and an increased rate of MFC nymphal mortality was due to adult feeding. Field parasitism reached up to 32.7% emergence in Alstonville, New South Wales, Australia. We report on the parasitoid performance in native Australia, rearing biology, host specificity testing, and the extant natural enemies associated with MFC in Hawaii. A petition to release this parasitoid for the biocontrol of MFC in Hawaii is pending. Once permitted for release, the colony will be shared with South African Mac Nut Association for their biocontrol program of this invasive pest. They will conduct their own testing before approval for release.

The relative dominance of surface oxygen content over pore properties in controlling adsorption and retrograde behavior of gaseous toluene over microporous carbon

The adsorption potential of activated carbon (AC) derived from macadamia nut shells (product code of Procarb-900: namely, AC-P) has been investigated using gaseous toluene as the target pollutant. The powder AC-P with high-microporosity (96%) and oxygen content (5.62%) exhibited very high adsorption capacity (214 mg·g−1) and partition coefficient (PC: 25 mol·kg−1·Pa−1) against 100 ppm (10 Pa) toluene at 99% breakthrough levels (1 atm dry N2). The factors governing toluene adsorption were explored with respect to the key variables such as surface functional groups, pore size distribution, sorbent bed mass (50, 100, and 150 mg), and particle size (i.e., 0.212–0.6 mm (powder AC: PAC)) vs. 0.6–2.36 mm (granular AC: GAC)). Accordingly, the adsorption process was physical, mainly due to the non-polar interactions (i.e., π-π interactions) between the adsorbent and adsorbate molecules. The high affinity of AC-P at low breakthrough levels was obtained through a combination of smaller particle size (PAC) and larger adsorbent mass (i.e., 150 mg) with the appearance of a very pronounced retrograde phenomenon (e.g., at < 1% breakthrough level). As such, toluene adsorption appeared to be affected more sensitively by particle size and adsorbent mass (especially at low breakthrough levels) than by high microporosity. Most importantly, the oxygen content of AC emerges as one of the key factors governing the maximum capacity, as the changes in pore volume are not crucial to explain the observed adsorption patterns of toluene.

Impact of Preharvest Ethephon Foliar Spray on the Postharvest Fatty Acid Profile and Dietary Indicators of Macadamia Nuts

The use of ethephon, designed to stimulate nut detachment, initiates the release of ethylene, a well-established regulator of postharvest shelf-life in various agricultural products. This study aimed to assess the impact of ethephon application on individual fatty acids and dietary indicators in two macadamia nut cultivars, namely ‘788’ and ‘Beaumont,’ during postharvest storage. Nuts that naturally abscised and those detached through ethephon treatment were divided into two groups: the ethylene-treated group (ED) and the control group (CD). Nuts were stored at 25 °C and sampled at 0, 36, and 72 days for fatty profile analysis. Our findings indicated a significant increase in stearic acid content in ED nuts (24,622 µg/g) compared to CD nuts (16,764 µg/g) at the end of the storage period for the ‘Beaumont’ cultivar. Additionally, unsaturated fatty acids (USFAs), such as eicosatrienoic acid + erucic acid (C20:3n3 + C22:1) and eicosatrienoic acid + alpha-linolenic acid (C20:1 + C18:3n3), were notably reduced. Hierarchical clustering analysis revealed positive correlations between ethylene treatment and saturated fatty acids (SFAs) in both ‘Beaumont’ (0.78) and ‘788’ (0.80) cultivars. This also coincided with an increase in atherogenic indices, thrombogenic index, and saturation index and a decrease in the hypocholesterolemic/hypercholesterolemic ratio and arachidonic acid (C20:4n6) within the ED group of the ‘Beaumont’ cultivar, collectively potentially impacting nutritional quality negatively. Furthermore, our findings indicated that the PUFA:SFA ratio was higher in CD (0.51) compared to ED (0.45) on day 72 for the ‘Beaumont’ cultivar, revealing differences in fatty acid compositions between the two treatment groups. Conversely, for ‘788’, both ED and CD had a PUFA:SFA ratio below 0.45, indicating an increased risk of cardiovascular diseases. These results suggest that ethephon treatment increases SFA levels and reduces USFA levels in the ‘Beaumont’ cultivar, while the response to ethylene varies between the two cultivars. Thus, the study provides insight into the significant role of modifying ethephon treatment methods and careful cultivar selection in the attainment of optimal nutritional value and shelf-life of macadamia nuts.