Turkish hazelnuts: Properties and effect of microbiological and chemical changes on quality

Presence of aflatoxins in hazelnut paste in Turkey and a risk assessment study

Two hundred and two hazelnut paste samples from various hazelnut processing plants in the Black Sea Region of Turkey were analysed for the incidence of aflatoxins (AFs) by liquid chromatography coupled with fluorescence detection (LC-FLD). All 202 (100%) hazelnut paste samples were contaminated with various AFs ranged from 0.17 to 12.96 µg kg^-1. AF contamination level of four (1.98%) samples exceeded legal limits. Risk assessment for hazelnut paste was determined by using AF incidence results, and the margin of exposure (MOE) and hepatocellular carcinoma (HCC) risk approach were applied. For the adult Turkish population (15+ years age group), the average lower bound (LB) and upper bound (UB) exposure levels for aflatoxin B1 (AFB1) and total aflatoxins (AFT) were 0.0106-0.0107 ng kg^-1 body weight (bw) per day and 0.0250 ng kg^-1 bw per day, respectively. MOE estimates for mean and 95th percentile exposures to AFB1 for hazelnut paste were higher than 10,000, which indicates no potential health concern for Turkish adults. HCC for the Turkish population was 0.00023 cases per 100,000 people per year. The study indicates that Turkish population is not under this toxicological risk when consuming hazelnut paste containing food products.

Effect of Drying Temperatures and Exposure Times on Aspergillus flavus Growth and Aflatoxin Production on Artificially Inoculated Hazelnuts

ABSTRACT

Aspergillus flavus may colonize hazelnuts and produce aflatoxins in the field and during storage. The main purpose of this study was to investigate the influence of drying temperature and exposure times on the viability of A. flavus and its ability to produce aflatoxins during the drying process and storage. Hazelnuts were inoculated with A. flavus and dried at different temperatures to reach 6% moisture content and a water activity (aw) of 0.71, a commercial requirement to avoid fungal development and aflatoxin contamination. Hazelnuts were dried at 30, 35, 40, 45, and 50°C and subsequently stored at 25°C for 14 days. After drying at 30, 35, and 40°C, increased amounts of A. flavus were evident, with the highest concentration occurring after drying at 35°C ([6.1 ± 2.4] × 106A. flavus CFU/g). At these temperatures, aflatoxins were detected only at 30 and 35°C. Aflatoxins, however, were present at higher levels after drying at 30°C, with concentrations of 1.93 ± 0.77 μg/g for aflatoxin B1 (AFB1) and 0.11 ± 0.04 μg/g for aflatoxin B2 (AFB2). After 14 days of storage, the highest A. flavus concentration and the highest levels of mycotoxins were detected in samples treated at 35°C ([8.2 ± 2.1] × 107A. flavus CFU/g and 9.30 ± 1.58 μg/g and 0.89 ± 0.08 μg/g for AFB1 and AFB2, respectively). In hazelnuts dried at 45 or 50°C, no aflatoxins were found either after drying or storage, and a reduction of A. flavus viable conidia was observed, suggesting that a shorter and warmer drying is essential to guarantee nut safety. The lowest temperature that guarantees the lack of aflatoxins should be selected to maintain the organoleptic quality of hazelnuts. Therefore, 45°C should be the recommended drying temperature to limit A. flavus growth and aflatoxin contamination on hazelnuts.

HIGHLIGHTS

Lipid Characterization of Chinese Wild Hazelnuts (Corylus mandshurica Maxim.)

To develop and use the hazelnut, the main composition, and the physicochemical characteristics, fatty acid compositions, triacylglycerol (TAG) distribution and tocol contents of Hazelnut (Corylus mandshurica Maxim.) which growing in Changbai mountain of Jilin province (HO1) and Anshan city of Liaoning province (HO2) in China were investigated, and the comparative study between the two hazelnut oils and American hazelnut / Turkish hazelnut were also explored. The content of crude lipid and protein in HO1 and HO2 were approximately 54% and 17%, 55% and 16%, respectively. The two hazelnut oils were abundant in unsaturated fatty acids, with the primary unsaturated fatty acids were oleic acid (78%-80%) and linoleic acid (14-16%), which accounted for above 90% of the oils. Therefore, both of the hazelnut oils were important sources of essential fatty acid. In addition, the main saturated fatty acid of the two hazelnut oils were palmitic acid (3%) and stearic acid (1-2%). The main triacylglycerols (TGA) profile were dioleolinolein (OOL), oleodilinolein (OLL) and triolein (OOO). The contents of tocol were 574.44 μg/g, 647.49 μg/g oil in HO1 and HO2, respectively, both of them were higher than that of grape seed oils (454 μg/g), olive oils (209 μg/g) and walnut oils (255 μg/g). The total phytosterol contents were over 2000μg/g and β-sitosterol was the most predominant sterol in two oils.

New Taste-Active 3-( O-β-d-Glucosyl)-2-oxoindole-3-acetic Acids and Diarylheptanoids in Cimiciato-Infected Hazelnuts

Activity-guided fractionation in combination with sensory analytics, LC-TOF-MS, and 1D/2D-NMR spectroscopy enabled the identification of the bitter tasting diarylheptanoids asadanin, giffonin P, and the previously not reported ( E)-7,9,10,13-tetrahydroxy-1,7-bis(2-hydroxyphenyl)hept-9-en-11-one and 4,12,16-trihydroxy-2-oxatricyclo[13.3.1.1^3,7]-nonadeca-1(18),3,5,7(20),8,15,17-heptaen as well as the yet unknown astringent compounds 2-(3-hydroxy-2-oxoindolin-3-yl) acetic acid 3- O-6'-galactopyranosyl-2″-(2″oxoindolin-3″yl) acetate and 3-( O-β-d-glycosyl) dioxindole-3-acetic acid in Cimiciato-infected hazelnuts exhibiting a bitter off-taste. Quantitative LC-MS/MS studies, followed by dose/activity considerations confirmed for the first time asadanin to be the key contributor to the bitter taste of Cimiciato-infected hazelnuts. Furthermore, quantitative studies demonstrated that neither the physical damage alone nor a general microbial infection is able to initiate a stress-induced asadanin generation, but most likely either specific Cimiciato-specific microorganisms associated with the bugs or specific chemical stimulants in the bugs' saliva is the cause triggering asadanin biosynthesis. Finally, also germination was found for the first time to activate diarylheptanoid biosynthesis, resulting in higher contents of bitter tasting phytochemicals and development of the bitter off-taste.

Within-Plant Distribution and Susceptibility of Hazelnut Cultivars to Mikomya coryli (Diptera: Cecidomyiidae)

The Mikomya coryli (Kieffer) (Diptera: Cecidomyiidae) is widespread in Europe and the most important cecidomyiid pest of hazelnut. Within-plant distribution, susceptibility of 18 Turkish hazelnut cultivars ('Acı,' 'Allahverdi,' 'Çakıldak,' 'Cavcava,' 'Foşa,' 'İncekara,' 'Kalınkara,' 'Kan,' 'Karafindık,' 'Kargalak,' 'Kuş,' 'Mincane,' 'Palaz,' 'Sivri,' 'Tombul,' 'Uzunmusa,' 'Yassı Badem,' and 'Yuvarlak Badem'), and the phenology of larvae of this pest in hazelnut leaves and involucres were assessed in 2014 and 2015 in Giresun (Turkey). Mikomya coryli distribution differed significantly within different parts of the hazelnut plant. The highest gall numbers of M. coryli were found in the middle part (0.70-1.40 m) of the plant in both years. Total gall numbers varied between years: 1,779 and 2,588 galls were counted in 2014 and 2015, respectively. Susceptibility to M. coryli damage varied significantly among the cultivars. The highest leaf gall densities and total numbers of galls were found on leaves and involucres of Allahverdi, Yuvaklak Badem, and Yassı Badem cultivars in both years. Mikomya coryli larvae were detected between April and June in the leaf galls. The number of larvae in the involucres changed between April and mid-June. Results of the within-plant distribution, M. coryli larval phenology, and cultivar pest-susceptibility analyses are presented to enable effective control of the pest as a part of hazelnut integrated pest management.

Influence of Different Hazelnut Cultivars on Some Demographic Characteristics of the Filbert Aphid (Hemiptera: Aphididae)

The filbert aphid Myzocallis coryli (Goeze) is a serious pest of hazelnut in North America, Italy, Spain, and Turkey. To evaluate the resistance of hazelnut to this insect, aphids were reared on five major cultivars ('Tombul,' 'Palaz,' 'Çakıldak,' 'Foşa,' and 'Mincane') under laboratory conditions. The developmental times of preadult and adult stages, total longevity, reproduction, and life table parameters were analyzed according to age-stage, two-sex life table theory, in which the stage differentiation and variable developmental rates among individuals could be described. The intrinsic rate of increase (r) and finite rate of increase (λ) varied among the cultivars. The highest values were found for aphids reared on Çakıldak (r = 0.2019 d-1, λ = 1.2238 d-1), which did not differ significantly from Mincane (r = 0.1957 d-1, λ = 1.2161 d-1), whereas these parameters were lowest for Palaz (r = 0.1622 d-1, λ = 1.1761 d-1) and Foşa (r = 0.1677 d-1, λ = 1.1826 d-1). Based on longer preadult development time, shorter adult longevity, shorter reproductive period, together with the demographic parameters, Palaz and Foşa provide a relatively unfavorable environment for the filbert aphid. The results obtained from demographic data together with estimates of pest growth potential generated by computer projection based on age-stage, two-sex life table theory, demonstrate that both Palaz and Foşa are resistant cultivars for M. coryli and can be considered in hazelnut integrated pest management and hazelnut breeding programs.

The Cyclic Diarylheptanoid Asadanin as the Main Contributor to the Bitter Off-Taste in Hazelnuts (Corylus avellana L.)

Activity-guided fractionation and taste dilution analysis (TDA), followed by LC-MS/MS, LC-TOF-MS, and 1D/2D-NMR spectroscopy, led to the identification of the cyclic diarylheptanoid asadanin exhibiting a human bitter recognition threshold of 13 μmol/kg, as the major inducer of the sporadic bitter off-taste of hazelnut kernels (Corylus avellana L.). Sensory analysis of hazelnut samples from two origins (Ordu/2013 and Akçakoca/2014) and from Cimiciato-infected hazelnut kernels, followed by LC-MS/MS quantitation of 1 and calculation of dose-over-threshold (DoT) factors, showed established evidence for the Cimiciato infection as the major inductor of asadanin biosynthesis in hazelnut kernels and, as a consequence, as the reason for bitter off-taste development.

Quality changes in macadamia kernel between harvest and farm-gate

BACKGROUND

Macadamia integrifolia, Macadamia tetraphylla and their hybrids are cultivated for their edible kernels. After harvest, nuts-in-shell are partially dried on-farm and sorted to eliminate poor-quality kernels before consignment to a processor. During these operations, kernel quality may be lost. In this study, macadamia nuts-in-shell were sampled at five points of an on-farm postharvest handling chain from dehusking to the final storage silo to assess quality loss prior to consignment. Shoulder damage, weight of pieces and unsound kernel were assessed for raw kernels, and colour, mottled colour and surface damage for roasted kernels.

RESULTS

Shoulder damage, weight of pieces and unsound kernel for raw kernels increased significantly between the dehusker and the final silo. Roasted kernels displayed a significant increase in dark colour, mottled colour and surface damage during on-farm handling.

CONCLUSION

Significant loss of macadamia kernel quality occurred on a commercial farm during sorting and storage of nuts-in-shell before nuts were consigned to a processor. Nuts-in-shell should be dried as quickly as possible and on-farm handling minimised to maintain optimum kernel quality.

Identification of prenyl ethyl ether as a source of metallic, solvent-like off-flavor in hazelnut

In a large batch of ground hazelnuts, a metallic, solvent-like off-note was detected. In this investigation, the volatiles from the batch showing off-notes were compared to a batch without off-notes. On the basis of gas chromatography (GC) sniffing and instrumental analysis, a terpenoid compound, prenyl ethyl ether, was identified as a key contributor to the off-note. The compound was quantified, and its contribution to the metallic, solvent-like off-flavor was confirmed by spiking experiments and sensory evaluation. Analytical and sensory experiments found that the off-note was still present in hazelnut cakes. Fat oxidation did not contribute to the off-flavor. Analysis of market products demonstrated the correlation between the identified terpenoid and the off-flavor. It is assumed that fungi are involved in off-flavor formation.

Dropping macadamia nuts-in-shell reduces kernel roasting quality

BACKGROUND

Macadamia nuts ('nuts-in-shell') are subjected to many impacts from dropping during postharvest handling, resulting in damage to the raw kernel. The effect of dropping on roasted kernel quality is unknown. Macadamia nuts-in-shell were dropped in various combinations of moisture content, number of drops and receiving surface in three experiments. After dropping, samples from each treatment and undropped controls were dry oven-roasted for 20 min at 130 °C, and kernels were assessed for colour, mottled colour and surface damage.

RESULTS

Dropping nuts-in-shell onto a bed of nuts-in-shell at 3% moisture content or 20% moisture content increased the percentage of dark roasted kernels. Kernels from nuts dropped first at 20%, then 10% moisture content, onto a metal plate had increased mottled colour. Dropping nuts-in-shell at 3% moisture content onto nuts-in-shell significantly increased surface damage. Similarly, surface damage increased for kernels dropped onto a metal plate at 20%, then at 10% moisture content.

CONCLUSION

Postharvest dropping of macadamia nuts-in-shell causes concealed cellular damage to kernels, the effects not evident until roasting. This damage provides the reagents needed for non-enzymatic browning reactions. Improvements in handling, such as reducing the number of drops and improving handling equipment, will reduce cellular damage and after-roast darkening.

Turkish Tombul hazelnut (Corylus avellana L.). 1. Compositional characteristics

The quality of Tombul (Round) hazelnut, grown in the Giresun province of Turkey, was determined by measuring proximate composition, minerals, vitamins, dietary fiber, amino acids, and taste active components (free amino acids, sugars, and organic acids). Fat was the predominant component in Tombul hazelnut (approximately 61%). The major minerals were potassium, phosphorus, calcium, magnesium, and selenium. Hazelnut was also found to serve as an excellent source of vitamin E (24 mg/100 g) and a good source of water soluble (B complex) vitamins and dietary fiber. The major amino acids were glutamic acid, arginine, and aspartic acid. The three nonessential amino acids and the essential amino acids contributed 44.9 and 30.9% to the total amino acids present, respectively, while lysine and tryptophan were the limiting amino acids in Tombul hazelnut. Twenty-one free amino acids, six sugars, and six organic acids were positively identified; among these, arginine, sucrose, and malic acid predominated, respectively. These taste active components may play a significant role in the taste and flavor characteristics of hazelnut. Thus, the present results suggest that Tombul hazelnut serves as a good source of vital nutrients and taste active components.

Turkish Tombul hazelnut (Corylus avellana L.). 2. Lipid characteristics and oxidative stability

The quality of crude hazelnut oil extracted from Tombul (Round) hazelnut, grown in the Giresun province of Turkey, was determined by measuring lipid classes, fatty acids, and fat soluble bioactives (tocopherols and phytosterols). Oxygen uptake, peroxide value, thiobarbituric acid reactive substances, and alpha-tocopherol levels of stripped and crude hazelnut oils in bulk and oil-in-water (o/w) emulsion systems were also evaluated as indices of lipid oxidation over a 21 day storage period at 60 degrees C in the dark. The total lipid content of Tombul hazelnut was 61.2%, of which 98.8% were nonpolar and 1.2% polar constituents. Triacylglycerols were the major nonpolar lipid class and contributed nearly 100% to the total amount. Phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol were the most abundant polar lipids, respectively. Sixteen fatty acids were identified, among which oleic acid contributed 82.7% to the total, followed by linoleic, palmitic, and stearic acids. Unsaturated fatty acids accounted for 92.2% of the total fatty acids present. Among oil soluble bioactives, alpha-tocopherol (38.2 mg/100 g) and beta-sitosterol (105.5 mg/100 g) were predominant in hazelnut oil and comprised 88 and 93% of the total tocopherols and phytosterols present, respectively. The results also showed that both stripped and crude hazelnut oils were more stable in terms of lipid oxidation in the bulk oil as compared to those in an o/w emulsion.

Detection of hazelnut oil adulteration using FT-IR spectroscopy

Fourier transform infrared spectroscopy (FT-IR) was used to detect the adulteration of hazelnut oil with different types of oils and to detect the adulteration of extra-virgin olive oil with hazelnut oil. Spectra of hazelnut oil, seven other types of oils, extra-virgin olive oil, and the adulterated oils were collected with a FT-IR equipped with a ZnSe-ATR accessory and a MCTA detector. Discriminant analysis and partial least-squares analysis were used to analyze the data. Classification of hazelnut oil, olive oil, and the other types of oils was achieved successfully with FT-IR. The detection level for sunflower oil adulteration of hazelnut oil was 2%, and the correlation coefficient for the PLS model was 0.99. Adulteration of virgin olive oil with hazelnut oil could be detected only at levels of 25% and higher.