The Comparison Of Walnut Comprehensive Quality From Seven Main Production Areas In China

The cultivation areas and production of China's walnut have been ranked 1st in the world.The key to improving the efficiency of walnut industry is the walnut quality.The nutritional and safety qualities of 185 walnut samples collected from seven main producing areas of China?Xinjiang,Hebei,Gansu,Henan,Shanxi,Guangxi and Sichuan?were analyzed.Based on the data,firstly,the comprehensive qualities and spatial distribution of walnuts were defined.Secondly,the differences between the comprehensive qualities of Juglans sigillata Dode and Juglans regia L.were compared.Thirdly,the characteristic components of walnut quality were proposed by the combination of principal component analysis with random forest method.Finally,quantitative evaluation models for the integrated quality of walnut were established,which could be applied for the quantitative evaluation of walnut quality.The results about the nutritional qualities are as following.Vitamin E,fatty acid composition,total phenolics,total flavonoids,and mineral elements were determined by high performance liquid chromatography,gas chromatography,visible spectrophotometry,and inductively coupled plasma mass spectrometry.The results showed that the fat contents of walnut samples in seven main producing areas of China were ranged from 63.96%to 65.39%.Linoleic acid was the most abundant fatty acid,constituting from 41.84%to 69.01%.The kernels showed that high levels of potassium,phosphorus,magnesium and calcium,in which the contents were ranged from 689.93 mg/kg to 6062.56 mg/kg.The concentrations of trace elements such as manganese,iron,zinc,copper,molybdenum,cobalt,and selenium were ranged from 0.01 mg/kg to 115.00 mg/kg.This study found that the total polyphenols and the flavonoids concentrations of walnuts ranged from 0.82 g/100g to 9.85 g/100g and 0.32 g/100g to 4.52 g/100g,respectively.Significant differences?p<0.05?were found in chemical compositions among the seven walnut production areas in China.Vanadium contents showed the highest coefficient of variation in all samples and,in contrast,the lowest coefficients of variation were from linoleic acid,magnesium and protein contents.The results about safety qualities are as following.The contents of As,Pb,Cd,and Cr from 7 Provinces in China were analysed by inductively coupled plasma mass spectrometry?ICP-MS?.Levels of heavy metals in walnuts do not pose a serious contamination from 7provinces of China.The concentrations of four heavy metals?As,Pb,Cd,Cr?were ranged ND⁰.064 mg/kg?ND⁰.095 mg/kg?ND⁰.017 mg/kg?ND².314 mg/kg,respectively.These concentrations did not exceed the MRLs of LY/T 1777-2008?Forest Food-General rule for quality safety?.The values of nemero pollution index for heavy metals were 0.578?Sichuan?,0.413?Guangxi?,0.390?Gansu?,0.359?Xinjiang?,0.353?Henan province?,0.310?Hebei?,and 0.289?Shanxi?.The order for heavy metals contamination was chromium>arsenic>lead>cadmium.Based on the exposure health risk assessment model recommended by the United States Environmental Protection Agency?USEPA?,the consumer risk assessment for walnut consumption was evaluated.The hazard quotients for arsenic,lead,and chromium were 7.32×10^-3?4.65×10^-4?1.97×10^-4,respectively.From public health point of view,the observed levels of heavy metals in walnuts do not pose a serious health risk to the consumers.The comparison for the integrated qualities of two kinds of walnuts showed that there were significantly differences between walnuts?Juglans regia L.?and walnuts?Juglans sigillata Dode??p<0.05?in contents of total polyphenols,flavonoids,linolenic acid,potassium,magnesium,phosphorus,titanium,aspartic acid,serine,glycine,valine,isoleucine,leucine,histidine,arginine and vitamin E.Among them,vitamin E,potassium,and titanium had the highest variation.In addition,the contents of vitamin E,potassium,and titanium in walnut?Juglans regia L.?were rangded from 23.19-58.13 mg/100g,2907.14⁵795.60 mg/kg,and 12.95³6.40 mg/k,respectively.Besides,the contents of vitamin E,potassium,and titanium in walnut?Juglans sigillata Dode?were rangded from 27.99⁵0.06 mg/100g,3626.071⁶606.56 mg/kg,and 23.55⁴4.78 mg/kg,respectively.Although both the principal component analysis and the random forest method are suitable for the establishment of a quantitative model for integrated quality of walnut,the random forest method can solve the modeling problems of collinearity,nonlinearity and index ratios.Especially,the result of random forest method is more intuitive and objective.Based on the random forest method and the statistical test,the characteristic chemical constituents of qualities?including molybdenum,vanadium,cysteine,vitamin E,potassium,titanium,total phyphenols,selenium,flavonoids,palmitic acid,copper,iron,sodium,boron,stearic acid?were determined,which were the key to comparing difference among walnut qualities.Thus,based on these characteristics of quality differences,a quantitative model for integrated quality of walnut was established,which was then applied for the evaluation of the integrated qualities of walnut from different areas.The sort order was as following:Xinjiang,Sichuan,Gansu,Henan,Guangxi,Hebei and Shanxi.Above all,the discriminant correctness rate of the walnut production areas in 7 production areas exceeds 97%,which was based on the principal component analysis and the random forest method.