Discrimination of almonds (Prunus dulcis) geographical origin by minerals and fatty acids profiling

Abstract Twenty-one almond samples from three different geographical origins (Sicily, Spain and California) were investigated by determining minerals and fatty acids compositions. Data were used to discriminate by chemometry almond origin by linear discriminant analysis. With respect to previous PCA profiling studies, this work provides a simpler analytical protocol for the identification of almonds geographical origin. Classification by using mineral contents data only was correct in 77% of the samples, while, by using fatty acid profiles, the percentages of samples correctly classified reached 82%. The coupling of mineral contents and fatty acid profiles lead to an increased efficiency of the classification with 87% of samples correctly classified.


Introduction
The almond is a nut, widely used as a raw or toasted ingredient in many desserts, ice cream, cake, pastry and milk. They are typically high in fat but their fatty acid composition is advantageous in relation to risk of coronary heart disease (Sabate et al. 1996;Bach et al. 2013;Lei et al. 2014). Almond lipids, about 55% of the nut weight, contain 92% unsaturated fatty acids, possibly contributing to the cardio protective effect of a diet rich in nuts (Maguire et al. 2004). Considering the high nutritive value of almonds, the knowledge of its chemical ABSTRACT Twenty-one almond samples from three different geographical origins (Sicily, Spain and California) were investigated by determining minerals and fatty acids compositions. Data were used to discriminate by chemometry almond origin by linear discriminant analysis. With respect to previous PCA profiling studies, this work provides a simpler analytical protocol for the identification of almonds geographical origin. Classification by using mineral contents data only was correct in 77% of the samples, while, by using fatty acid profiles, the percentages of samples correctly classified reached 82%. The coupling of mineral contents and fatty acid profiles lead to an increased efficiency of the classification with 87% of samples correctly classified.
composition would enable to establish both quality and consumption criteria, due to the incidence of some compositional parameters on the nutritional and health values of almond kernels (for example saturated/unsaturated fatty acid ratio) (Piscopo et al. 2010). Moreover, almond industry demands commercial characterised by kernels with high-quality attributes (Berger 1969;Yada et al. 2011). Considering both fundamental economic implications of any fraud and food authenticity as one of the most crucial issues in food control and safety, it is necessary to develop a chemical methodology that can confirm food labels identifying geographic origin. Most of these studies characterised the almond about organic content by analysing essential oils (Tiên et al. 2015), fatty acid (Maestri et al. 2015) or phytosterols (Zhu et al. 2015). In particular, we have planned to study the mineral content (Na, K, Li, Ca, Mg, Al, etc.) and fatty acid composition of 21 almond samples from Sicily, Spain and California (Table  S1). Collected data will be treated by LDA to assess whether the mineral profile alone, or in combination with the fatty acid profile, could lead to a fast and correct classification of the geographical origin of almonds. Use of mineral contents coupled at fatty acids profiles could provide an alternative solution at classic discrimination origin procedures. In this paper, we report the first monitoring campaign of minerals and fatty acids content in Sicilian almonds also, we present the first one study on discrimination of the almonds origins by using chemometric analysis (linear discrimination analysis) based on fatty acids and minerals contents in Sicilian almond compared to those Californian and Spanish.

Results and discussion
In Tables S3 and S4 report the fatty acid profiles and minerals contents (on a dry weight basis), respectively, for the 21 analysed samples. Considering the mean values, in almond oil, as reported throughout the literature (Sabate et al. 1996;Ayadi et al. 2006), the four major fatty acids, in decreasing order, are oleic (C 18:1 ), linoleic (C 18:2 ), palmitic (C 16:0 ) and stearic (C 18:0 ). Oleic acid was the most abundant fatty acid, not reporting marked differences among samples from different areas. The oleic acid content ranged from 53 to 86%. The mean value was 66% and the highest percentage was found in a Californian sample (C17). Linoleic acid content ranged from 10 to 31%. The mean value was 22% with the highest value founded in a Sicilian sample (Ci11). In good agreement to the literature data, in analysed almonds grown in various regions, oleic and linoleic acids account for about 90% of the total lipid, and saturated fatty acid levels are very low (meanly 8.9%) (Sabate et al. 1996). Our data, in agreement to the literature, found that the oleic acid content is highly and negatively correlated with the linoleic acid levels. The oleic/linoleic (O/L) ratios ranged from 1.9 to 8.5 with an average of 3.5. Considerable variability in O/L ratios among almond samples has been observed. In particular, the mean O/L values were 3.8 and 3.0 for foreign and Sicilian samples, respectively. Sicilian almonds differ from the other samples by the low value of oleic and palmitoleic acids ratio (O/P); in the first case, the mean value was 180 while for foreign almonds was 268. The content of palmitic acid ranged from 2.9 to 9.6%. The mean value was 6.5%with the highest value founded in a Sicilian sample (Ci12). In good agreement with other studies (Askin et al. 2007), we have found negative proportional relationship between the oleic and linoleic acids. Relations are shown in Figure S2. Considering all the Sicilian samples, the mean ratio between unsaturated and saturated fatty acids was about 10%, while considering foreign almonds the mean value ratio was higher (about 15%). Myristic, linolenic, arachidonic and arachidic acids were present in all samples (except a Spanish sample containing 2.3% of linolenic acid) in trace amounts. Similarly to other seeds (Satil et al. 2003;Tsantili et al. 2010), these minor acids do not exceed 0.5%. Table S3 shows the concentration values of K, Li, Sr, Na, Ca, Mg and Al in the samples. The sodium content of the almond samples ranged from 62 to 1494 mg kg −1 with average of 415 mg kg −1 . Potassium was detected in all analysed almonds and the concentration ranged from 208 to 6236 mg kg −1 . The highest content was found by us in a Sicilian sample (C17). The mean K concentration was 2150 mg kg −1 . The lithium content in analysed samples ranges from 0.5 to 11 mg kg −1 . The mean value was 4.4 mg kg −1 and the highest Li concentration was found in a Sicilian sample (Ci23). The strontium concentration in analysed samples ranged from 0.2 to 9.1 mg kg −1 . The highest strontium content was found in a Sicilian sample (Ci23) and the lowest (0.2 mg kg −1 ) in a Spanish sample (sample Cs25).The concentration of calcium in almond samples ranged from 154 to 5686 mg kg −1 . The mean value was 2096 mg kg −1 . The highest values were detected in a Sicilian sample Ci23.The range of magnesium values found in samples was 197-5286 mg kg −1 . The mean value was 2650 mg kg −1 . The highest values were detected in a Californian sample (Cc27). The aluminium content of the almond samples ranged from 10 to 125 mg kg −1 with average of 28 mg kg −1 and is in agreement to those (0.4-13 mg kg −1 ) determined by some authors (López et al. 2002) in cereals. In our case, the highest Al levels were measured in two Sicilian samples (Ci23 and Ci24) of the same geographical area. The lowest values (10-11 mg kg −1 ) were detected in several samples of different geographical origin. The discriminant analysis was conducted to three clusters (Sicilian, California and Spain) by using three different information types (see supplementary material). Aluminium is known to have neurotoxic effects. In the majority of the cases, greater the uptake of aluminium the older a personae becomes. Increased levels of aluminium in the brain also affect the catecholamine neurotransmitters, noradrenaline and dopamine, in the frontal cortex, hippocampus and cerebellum. High cumulative concentrations of Al absorbed over a lifetime produce an alteration in neuronal excitability, resulting in the erratic and convulsive effects seen in aluminium neurotoxicity.

Experimental
See supplementary material online.

Conclusions
The whole analytical procedure based on ICP-OeS and GC-MS analysis is rapid and easy, and includes advantages of low costs. Linear discriminant analysis based on fatty acid profiles and metals content has correctly classified the 87% of sample considered. Also, data here reported constitute the results of the first monitoring campaign of minerals and fatty acids content in Sicilian almonds.

Funding
Funding for this work was provide, in part, by grants ex 60% 2007 University of Palermo and the PON a3_00053; PLASS "Platform for Agrifood Science and Security".