Camellia Oil Quality Indices from seeds harvested in Pontevedra (NW Spain)

Vela P., García-Sartal C., Salinero C., González-García M.

Estación Fitopatológica de Areeiro, Diputación de Pontevedra, Subida a la Robleda s/n, 36153 Pontevedra, Spain. pilar.vela@depo.es

Introduction

      Camellia seed oil has been used in many oriental countries as edible oil since ancient times. Currently, its annual production is estimated at 260 000 tons (Li et al., 2012), with China, India, Sri Lanka, Indonesia and Japan being the world’s largest seed oil producing countries and Camellia japonica, C. sasanqua and C. oleifera being the major crop species (Sahari, Ataii and Hamedi , 2004). Figure 1 shows the fruit and seed of Camellia sasanqua.

Figure 1: Camellia sasanqua fruit and seed

      Camellia oil has been recognized as a source of vitamins A, B and E, essential fatty acids, primarily as oleic acid, and also polyunsaturated fatty acids such as omega-6 linoleic acid (Li et al., 2012).  In a previous work, Salinero et al. have characterized the triglyceride composition of oil from C. reticulata and C. japonica harvested in Galicia (North Western Spain) by nuclear magnetic resonance (NMR).  The results confirmed that oleic acid (approximately 75%) was the main fatty acid found in both C. reticulata and C. japonica, followed by linoleic, linolenic and saturated fatty acids (Salinero et al., 2011). Furthermore, other functional components, such as camellia saponins, squalene or polyphenolic compounds have been found in camellia oil.  All these compounds confer anti-tumour effects, blood lipid reduction, protection of liver and heart, antisepsis and anti-inflammation effects, atherosclerosis delaying, anti-oxidation activities and immune function regulation on the population (He et al., 2011).
      However, the number of double bonds in their composition, as with other vegetable oils, limits camellia oil stability. The compounds with higher levels of unsaturation are more susceptible to oxidation. Free radicals can be formed after abstraction of the hydrogen in the carbon-carbon double bond position that react with oxygen to form a peroxy radical. The peroxy radical could form a hydroperoxide after removing a hydrogen atom adjacent to a double bond from another lipid molecule, and so on (Fox and Stachowiak, 2007). For this reason, studies into the composition of camellia oil are required to obtain quality information about the oil in terms of stability. Different analytical methods, including iodine value (IV), acid value (AV) and peroxide value (PV), are used to assess the oil stability. The IV determination gives information about the unsaturation level of a lipidic material (Zhang Wei-guo, 2011). The AV is a measure of the free fatty acids content. It indicates the amount of free fatty acids released by hydrolysis and oxidation (Armenta et al., 2007). The PV assesses the hydroperoxide content (primary oxidation products) (Zhang Wei-guo, 2011, Armenta et al., 2007). Hydroperoxide compounds could decompose and form alcohols, aldehydes, free fatty acids and ketones, leading to the oil smelling and tasting rancid (Yu et al., 2007).
      This work studies and establishes for the first time, the quality indices of Galician camellia oils from 30 different Camellia japonica cultivars, two C. hybrid cultivars, one C. sasanqua cultivar and one C. grijsii. The aim of this work was to establish differences and similarities between Camellia cultivars with respect to their quality indices (iodine value, acid value and peroxide value), and to assess the edibility of the oils.

Materials and Methods

      All the chemicals and solvents used were of analytical grade.

      Camellia seed oils

      Seeds from 34 different camellia specimens, 30 Camellia japonica cultivars, 2 C. hybrids, 1 C. sasanqua cultivar and 1 C. grijsii, were harvested in the Galician region (North-western Spain). Table 1 shows the code of each sample, as well as the Camellia species and the location to which the samples belong.

Table 1: Sample and Camellia  specie and cultivar names

      The seeds were cleaned by hand to remove foreign materials and then washed with tap water. Cleaned seeds were dried at room temperature. After these treatments, the seeds were ground in a mill. Camellia japonica seeds obtained after removing from the fruit are shown in Figure 2.

Figure 2: Camellia japonica seeds used for oil extraction

      Camellia oil samples were obtained by cold-pressed extraction.  About 200 g of crushed seeds are loaded into a hydraulic press and pressed by mechanical means to extract the oil. The oil portions belonging to a given camellia specimen were blended and refined by settling followed by filtration. Filtration was performed through filter modules that were composed of activated carbon and cellulose fibres. Finally, refined oils were put into clean, dry, amber coloured glass bottles and kept at 15 °C until further analysis. From left to right, Figure 3 shows the camellia oil obtained after settling and after filtration.

Figure 3: Camellia oil obtained after settling (test tube at the left) and after filtration (test tube at the right)

      Chemical and physical methods

Moisture and volatile matter determination
      Moisture and volatile matter was determined gravimetrically according to the UNE-EN ISO 662-1998 standard method (ISO 662-1998, 2001) as the mass loss suffered by five millilitres of oil sample after heating in an oven at 103 ±2 °C. Determinations were performed in duplicate. Results were expressed as a mass percentage.

Density determination
      The density of the samples, expressed as the average value of six replicates, was determined as the measure of the oil mass per unit volume at 25 °C.

Acid value
      The acid value (AV) was determined by a standard titration procedure according to the UNE-EN ISO 660:2009 (ISO 660:2010, 2010).  An amount of 10 g of camellia oil was dissolved in a 50:50 mixture of ethanol (purity 96%) and diethyl ether (purity 99.9%). Finally, the acids in solution were titrated with 0.1 M KOH prepared in ethanol solution. Results were expressed as grams of oleic acid per 100 g of oil. These determinations were carried out in triplicate.

Iodine value
      The iodine value (IV) was calculated according to the standard method UNE-EN ISO 3961:2009 (ISO 3961:2009, 2012). Data were obtained from the analysis of each sample oils prepared in triplicate. About 0.20 g of sample oil was dissolved in a mixture of cyclohexane and glacial acetic acid (50:50). Finally, the excess of iodine generated after adding Wijs solution, potassium iodide and deionized water, was titrated with sodium thiosulphate. Results were expressed as grams of iodine per 100 grams of oil.

Peroxide value
      To determine the peroxide value (PV), a portable HANNA instruments® photometer HI 83730 (Guipúzcoa, Spain) equipped with a commercially available kit of reactive was used. Results, expressed as milliequivalents of oxygen per kilogram of oil, were calculated as the average value of three replicates of the same sample.

Results and discussion

      Experiments were developed to assess and establish the quality parameters and oxidation stability of the Camellia oil obtained from 34 different specimens.

        Physical analysis of camellia seed oil

      Oil extraction from camellia seeds was performed by cold-pressing at room temperature as has been described above. Table 2 shows the mean recovery percentage value, calculated as the ratio of the mass of extracted oil to the mass of seed material for each extraction step of the same sample, and multiplied by 100. As it can be seen, recovery percentages ranged from 4.2% to 30.4%. Yield data clearly show that sample labelled as 198-A (C. sasanqua) contains greater amounts of oil.

Table 2: Physical oil parameters (recovery percentage, density and moisture percentage)

^a SD: Standard deviation
^b Recovery (%) = (oil weight (g))/(seed weight (g))×100
^c ND: No data is given

      Table 2 also shows the density and moisture percentage data obtained after subjecting the samples to the analytical methods described elsewhere. Density values were found between 0.886 and 0.910 g mL-1. Minimal density differences between samples were found,  the average value being close to 0.900 g mL-1. Furthermore, the density data obtained were below water density (1.000 g mL-1). Density is a parameter which gives us information about the sample nature, the density value being inversely proportional to molecular weight, and directly proportional to the level of unsaturation of the analysed samples (Akbar et al., 2009). 
      Low moisture percentages ranging from 0.00% to 0.49% (see Table 2) were found in the oil samples analysed.  High water content could affect the ability of the sample to be filtered. Moreover, an excess of water could be a danger for the conservation of the samples, leading to oil rancidity and to a strange taste or smell (Robards et al., 1988, Nykter et al., 2006).

        Chemical analysis of camellia seed oil

      Chemical quality indices such as AV, IV and PV provide information about the quality and stability of the oils. Chemical data, obtained after subjecting the camellia oil samples to the analytical methodology previously described, are reported in Table 3.  
      Acid values (see Table 3) were found below 0.50 g oleic acid/100 g oil for most of the samples analysed. These data are consistent with the Codex Alimentarius specifications for extra virgin olive oil (less than 0.80 g oleic acid/100 g oil) (Codex Alimentarius, 1981). Seven out of the 28 studied samples showed much higher acid values (between 1.04-2.23 g oleic acid/100 g oil). This fact could be attributed to higher polyunsaturated fatty acids content in those oils, since acid value is positively correlated. 
      Comparable iodine values ranged from 75 to 88 g I2/100 g oil were found for the analysed samples (Table 3).  The data obtained matched that previously published for Camellia serniserrata Chi. oil (82.1 g I2/100 g oil) (Zhang Wei-guo, 2011). Furthermore, iodine values close to 80 g I₂/100 g oil were found in olive oil samples (Vigli et al., 2003). This is because camellia oil and olive oil are characterized by similar amounts of oleic acid and polyunsaturated fatty acids in their composition (Vigli et al., 2003).

Table 3: Chemical oil parameters (acid value, iodine value and peroxide value)

^a ND: No data is given
^b SD: Standard deviation of three replicates
^c meq: Milliequivalents

      Oils become rancid when the peroxide value is higher than 20 meq O2/kg oil. Therefore, considering that the peroxide values were within 0.0-8.5 meq O2/kg oil (Table 3); the samples analysed in this work can be regarded as oil of good quality. Differences in the peroxide values between the camellia oil samples could be attributed to their content of antioxidant compounds. Antioxidants are compounds that delay the autoxidation in samples by inhibiting or interrupting the formation of free radicals (Brewer, 2011). 
      It should be noted that low acid values (0.29-0.66 g oleic acid/100 g oil), high iodine values (84-86 g I2/100 g oil) and low peroxide values (0.0-2.0 meq O2/kg oil) were found in those samples with the highest oil recovery percentages (sample 16-A, sample 198-A and sample RT).  However, iodine and peroxide values are positively correlated; this enables us to conjecture that these above mentioned samples could be the richest in antioxidant compounds. From the point of view of productivity and quality, samples 16-A, 198-A and RT are the most appropriate for cultivation.

Conclusions

      This study provides information about the physico-chemical properties of different camellia oils obtained in Galicia after cold-pressed extraction from the seeds. The highest oil extraction yield was found for the sample labelled 198-A (30.4%) (C. sasanqua). Furthermore, all camellia oils analyzed showed similar density values, close to 0.900 g mL^-1, and low moisture percentages (0.00-0.45%). Chemical oil parameters indicated the high quality of the camellia oils, with low acid values for most samples (< 0.50 g oleic acid/100 g oil), iodine values ranging from 75 to 88 g I₂/100 g oil, and low peroxide values (< 9 meq O₂/ kg oil), guaranteeing the freshness of the oils. Physico-chemical parameters showed that samples 16-A, 198-A and RT were the most suitable for oil production.  

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