Variations in nutritional quality and fatty acids composition of sardine (Sardina pilchardus) during canning process in grape seed and olive oils

Abstract

Fish canning industries generally use different oils to ensure the juicing stage of canned sardines. In this context, we tested the use of grape seed oil (GSO) which could provide several health benefits to consumers. This study compared its effects on the quality of canned sardine to that of olive oil (OO). Total polyphenols, flavonoids and non flavonoids of the tested GSO were significantly higher than those of the OO. Also, The GSO was rich in polyunsaturated fatty acid (PUFA), namely linoleic acid (65.36% of total fatty acids). The use of GSO in the sardine sardines canning process increased significantly fat, protein and ash contents after 90 days of conservation. The fatty acid profile was dominated by PUFA for all the tested samples. Docosahexaenoic acid was the most abundant unsaturated fatty acid, followed by linoleic acid in GSO samples (20.86 ± 0.06% compared to 1.46 ± 0.05% in fresh sardine) and oleic acid in OO samples. Both atherogenic and thrombogenic indices decreased after the canning process in OO and GSO to less than 1. Thus GSO seems to improve the lipid nutritional quality in fresh sardine. In addition, the values for thiobarbituric acid and Total volatile base nitrogen did not exceed critical limits.

Introduction

Sardine is a small, oily, pelagic fish from the Clupeidae family distributed throughout the Mediterranean sea. Sardina pilchardus, Walbaum 1792 is a highly nutritive and the most important species of the Mediterranean fisheries (Soldo et al. 2019). In addition to the high protein digestibility of fish, sardine contains essential fatty acids and amino acids, minerals and vitamins necessary for healthy human diets. The nutritional importance of sardines is particularly related to polyunsaturated fatty acid (PUFA) namely omega-3 eicosapentaenoic (EPA; 20:5n-3) and docosahexaenoic (20:6n-3) fatty acids (FA), essential for human development, cardiovascular disease prevention and reducing harmful levels of cholesterol in plasma (Selmi et al. 2011). Nevertheless, oily fish is wellknown as a highly perishable food with limited shelf-life needs to be preserved. Therefore, the canning process is one of the most effective and widespread method of fish preservation. It includes cooking, cooling, packing with a covering medium (oil, tomato sauce) in hermetically sealed cans and sterilizing to achieve commercial sterility by the application of heat.

In Tunisia, canned sardine is widely consumed due to its ready availability and low cost. However, quality deterioration of canned fishery products is related to their high levels of nitrogen compounds and unsaturated fatty acids (Gu et al. 2001). Thus, the effect of canning on the chemical composition of marine products has been investigated in several studies.

Usually, vegetable oils (olive oil (OO), starch oil, sunflower oil, etc.…) are used for canning fish, but actually researchers have a special emphasis on finding new sources of vegetable oils, mainly from fruits seed considered as industrial by-products such as GSO (Parry et al. 2006).

Grape seed contain high contents of unsaturated fats and bioactive compounds with interesting properties namely antioxidant (Mahmoudi et al. 2018) and antimicrobial activities. Thus, it can be exploited for oil production and used as natural food preservatives (Rekik et al. 2016). Grape seed oil (GSO) was first manufactured in 1930 in Europe, and then it was used as cooking oil.

Cold press is considered as one of the best methods of extracting fruit seed oil since it protects bioactive components (Parry et al. 2006). GSO contains linoleic acid, tocopherols and carotenoids which help to combat cardiovascular diseases (Garavaglia et al. 2016). Also, it has anti-hypercholesterolemia, neuroprotective and hepatoprotective effects (Ismail et al. 2016).

Since GSO is rich in polyphenols, interest in its antioxidant and anti-inflammatory effects has increased (Ismail et al. 2016) and against apoptosis of pancreatic cells (Lai et al. 2014). Polyphenols (especially flavonoids) are powerful antioxidants that are characterized by their ability to inhibit the formation of free radicals and to counteract the oxidation of large molecules (Oueslati et al. 2016). In addition, this oil could be used as a food additive to combat pathogenic bacteria since it had bactericidal activity (high polyphenols content) on several pathogenic micro-organisms namely Bacillus subtitlis, E. coli, Listeria monocytogenes, Salmonella enteridis (Rekik et al. 2016).

The aim of this study was to analyze an innovative method for canning sardine and to compare the effect of GSO and OO on the nutritional characteristics (moisture, ash, crude proteins, total fats contents and the nutritional quality indices of lipids), fatty acids composition and the stability of fish lipids oxidation of canned sardines (Sardina pilchardus).

Material and methods

Fish sampling and experimental design

Fresh sardines (Sardina pilchardus) were purchased from a local fish landing center in Bizerte (northeastern Tunisia). Fish were then transported on ice (fish to ice ratio, 1:1) to the laboratory within 30 min where they were weighed, measured, de-headed and cleaned.

Other ingredients like OO were also procured locally. On the other hand, GSO was obtained from a grape cultivar (Carignan) of Vitis vinifera Linnaeus, 1753 from Grombalia (36°35′59.99" N 10°29′59.99" E), northern Tunisia. This oil was prepared in the laboratory (Fig. 1). Seed were manually separated, air-dried then ground with a coffee grinder (FP 3121 Moulinex) until a fine powder was obtained. The oil was extracted by cold pressing at temperature under 60 °C. Then, the seed extract was filtered, evaporated, and the oil was stored at room temperature (20 °C) in dark glass bottles for further analysis. The oil yield was 7.8%. It was determined as follow:

$$\mathrm{Oil}\mathrm{yield}=(\text{Oil,content,(g)/grape,seed,content})\times 100.$$ 3

During processing, sardine samples were divided into two batches, then were gutted, headed, and then went through the different stages of the canning process illustrated in Fig. 1. Sterilisation was done at 121.5 °C during 90 min. Sardines were canned either in olive or grape seed oil. Cans (10.5 × 5 × 2.2 cm; 120 g) from to the same lot of treated fish were opened (after 3 months), the liquid was carefully drained, and the meat portions were pooled, minced, and enclosed in filter paper to absorb the free liquid before analysis.

Fig. 1.

Flow diagram of the production of grape seed oil (a) and canned sardines (b)

Polyphenols and flavonoids contents in grape seed and olive oils

The total polyphenols, flavonoids and non flavonoids of tested oils were determined using the Folin Ciocalteu reagent (Dewanto et al. 2002). A 0.125-ml sample of a methanolic seed oil was added to 0.5 ml of purified water and 0.125 ml of the Folin–Ciocalteu reagent. The solution was mixed then left for 6 min before adding 1.25 mL of 7% Na₂CO₃ and purified water to adjust the volume to 3 ml. After incubation for 90 min at 23 °C, the absorbance versus a prepared blank was read at 760 nm. The calibration curve of gallic acid range was 50–400 mg/ml (R² = 0.999).

Proximate composition analysis

The biochemical composition of the fresh and canned sardine samples in different medium was analyzed. Moisture content was evaluated according to the AOAC method (1990) by drying in an oven at 105 °C, until constant weight.

The ash content was determined in samples by burning each one for 12 h in a muffle furnace at 525 °C according to the AOAC (1995) method.

Crude protein content was measured based on Kjeldahl procedure of total nitrogen (AOAC 1990). In addition, crude fats were extracted according to the method of Folch et al. (1957) by chloroform: methanol (2:1); the lipid fraction was determined gravimetrically. All results were expressed as mean percentage of the wet weight for three replicates.

Fatty acid analysis and nutritional quality of lipids

Fatty acid analysis was done for fresh sardine (Fs), canned sardine and crude GSO in triplicate.

Fatty acid methyl esters (FAME) were identified according to Lepage and Roy (1986) protocol. In brief, the analysis was done in a Varian Agilent 6890 N gas chromatograph (Agilent Technologies, Santa Clara, USA), equipped with an auto-sampler and fitted with a split/splitless injector and a flame ionization detector (FID). Separation was performed in an Innowax 30 × 0.25 capillary column (25 m × 0.25 mm i.d., film thickness) (Agilent Technologies, Santa Clara, USA). The temperature was programmed from 180 to 200 °C at 4 °C / min, kept for 10 min at 200 °C, heated to 210 °C at 4° C / min, and kept at 210 °C for 14.5 min using injector and FID at 250 °C. The fatty acid contents in the total lipids of the samples were estimated using C21:0 as an internal standard (10 mg/ml) based on the peak area ratio. The fatty acid sequences ranged according to their chromatographic retention times, and the values are given as percentages of total fatty acid methyl esters.

Nutritional quality indices of lipids were calculated based on fatty acid composition.

• Atherogenicity index: [(C12:0 + (4*C14:0) + (C16:0)] / [(∑n6 + ∑ n3 + ∑MUFA)] (Ulbricht and Southgate 1991).

• Thrombogenicity index: [(C14:0 + C16:0 + C18:0)] / [(0.5 * ∑MUFA) + (0.5 * ∑n6) + (3 * ∑n3) / (∑n6)] (Ulbricht and Southgate 1991).

Thiobarbituric acid index

Thiobarbituric acid (TBA) index was determined using the procedure of AOCS (1998). This method enables us to directly measure TBA in oils and fats without primary isolation of secondary oxidation products. This method can be applied to animal and vegetable fats and oils. Results are expressed as mg malonaldehyde/kg of oil.

Total volatile base nitrogen

Total volatile base nitrogen (TVBN) analysis was performed based on Conway micro diffusion and titration (Conway 1962).

Statistical analysis

Statistical analysis was done using SAS software (SAS 9.1.3, 2002–2003, Institute Inc., Cary, NC, USA). The comparison of all the tested parameters of fresh and canned sardine in the different filling oils, were tested using LSD means’s test at 5% with one-way ANOVA. All analysis were performed using data from triplicate results.

Results and discussion

Polyphenols and flavonoids contents in grape seed and olive oils

The levels of phenolics in the analysed oils are given in Table 1. Total polyphenols, flavonoids and non flavonoids are significantly higher in the purified GSO than OO (respectively 0.352, 0.261 and 0.092 mg GAE/g oil). These results were relatively higher than total phenolics contents of GSO from nine Tunisian varieties which ranged from 0.056 to 0.116 mg GAE/g oil (Harbeoui et al. 2018) but also of Spanish and Turkish samples (Garavaglia et al. 2016).

Table 1.

Phenolics levels in grape seed oil and olive oil

Phenolics	Grape seed oil	Olive oil
Total polyphenols	0.35 ± 0.04a	0.15 ± 0.01b
Total flavonoïds	0.26 ± 0.04a	0.06 ± 0.01b
Non flavonoïds	0.092 ± 0.04a	0.089 ± 0.02b

Total polyphenols content analyzed as gallic acid equivalent (GAE) mg/g of oil

Data are expressed as mean ± SEM; values with different letters in the same line are significantly different at p < 0.05

These bioactive molecules detected in GSO are also known as the minor components of the oil or the unsaponifiable fraction and play an important role in the oil stability. Variation in the levels of these bioactive molecules could be attributed to grape species and environmental factors (Harbeoui et al. 2018).

Proximate composition of canned sardines

After 90 days, proximate composition was evaluated in the canned sardine (Table 2). Results showed that the canning process reduced significantly water content of fresh sardines (p < 0.05). In fact, moisture contents averaged 40 ± 0.45% and 42 ± 0.05% respectively for sardine canned in GSO (GSOs) and in OO (OOs) (Table 2). These results could be explained by the fact that oil diffusion in meat is always accompanied by free water perfusions by osmosis from fish tissues and thus water decreases in canned fish. Our findings are consistent with those of Selmi et al. (2008).

Table 2.

Proximate composition of canned sardine

	Fs	GSOs	OOs	SEM	Pr > F
Moisture	75.00 ± 0.60a	40.00 ± 0.45c	42.00 ± 0.05b	0.22	< 0.0001
Ash	1.06 ± 0.06c	2.08 ± 0.04b	2.32 ± 0.05a	0.03	< 0.0001
Crude protein	78.30 ± 0.12c	83.00 ± 0.05a	80.00 ± 0.14b	0.14	< 0.0001
Total lipids	6.40 ± 0.12c	12.00 ± 0.14a	8.00 ± 0.45b	0.14	< 0.0001

Data are mean values of three replicates (g/100 g) ± standard deviation; the means followed by the same letter within a line were not significantly different by LSD means test at 5%

Fs fresh sardine; GSOs canned sardine in grape seed oil; OOs canned sardine in olive oil; SEM standard error of the mean

However, the ash content increased significantly after canning to reach in 90 days: 2.08 ± 0.04% for GSOs and 2.32 ± 0.05% for OOs (Table 2). This can be associated with the decrease of water level but mainly of the mineral contents in the tested oils. Indeed, grape seed contained considerable amounts of macro and micro elements namely calcium and iron as also found by Kilinc and Cakli (2004).

Table 2 also showed that the canning process increased protein contents for both covering oils since moisture content decreased after sterilization. Also, sardines canned in GSO contained the highest amount of proteins (83 ± 0.05%).

GSO contains high amounts of polyphenols (including phenolic acids and flavonoids) (Table 1), vitamin E, tocopherols and tocotrienols which are a powerful antioxidant which protect the cell membrane from oxidative damage and consequently prevent protein and lipid oxidation (Garavaglia et al. 2016).

After 90 days of storage, lipid levels increased especially for sardines canned in GSO. Indeed, the percentage reached 12 ± 0.14% against 6.4 ± 0.12% for fresh sardines and 8 ± 0.45% for OOs (Table 2). This increase is due to sample dehydration and the incorporation of oil into the muscle. Similar results were found with sardine samples canned in OO (Selmi and Sadok 2007).

Sardine contains highly unsaturated fatty acids which can be affected by the canning process. Therefore, lipid oxidation can induce losses on its quality leading to off-flavour components production. Nevertheless, polyphenols contained especially in GSO can prevent lipid oxidation. Our results are in line of those of Ramanathan and Das (1992), who found that some polyphenols (quercetin, myricetin and elagic acid) have potent effect against lipid oxidation.

Fatty acids composition of grape seed oil

The fatty acid composition of the Carignan seed oils is shown in Table 3. It was rich in PUFA, namely linoleic acid (65.36% of TFA).

Table 3.

Fatty acids composition of grape seed oil (% of total fatty acids)

Fatty acid		Relative abundance (%)
Myristic acid	C14:0	0.05 ± 0.08
Palmitoleic acid	C16:1 n7	0.06 ± 0.07
Palmitic acid	C16:0	11.83 ± 0.50
Linoleic acid	C18:2 n6	65.37 ± 0.40
Oleic acid	C18:1 n9	17.45 ± 0.80
Stearic acid	C18:0	5.17 ± 0.31
Arachidic acid	C20:0	0.04 ± 0.06
SFA		17.09 ± 0.23
MUFA		17.51 ± 0.43
PUFA		65.37 ± 0.40

An important presence of monounsaturated fatty acids (MUFA) was also detected with oleic acid (17.45% of TFA), but also saturated fatty acids (SFA) were distinguished by the high levels of palmitic and stearic acids (11.82 and 5.16% of TFA). Additionally, arachidic (C20:0) and myristic (C14:0) acids were found in the minor fraction of SFA.

Our findings were similar to those described by Harbeoui et al. (2018) for GSO extracted with hexane and Soxhlet apparatus from Tunisian grape varieties. The predominant fatty acid was the linoleic acid ranging from 64.77 to 75.37% of total fatty acids. Lachman et al. (2015) found also that linoleic acid was also the most abundant fatty acid and α‐linolenic acid was present only in very low quantities not exceeding 0.77 g/100 g, in seed oil from 23 grape varieties. In the cold‐pressed GSO, linoleic acid was also the most abundant fatty acids, contributing to between 66.0% and 75.3% TFA. Linoleic acid is directly related to the promotion of human health (Lutterodt et al. 2011).

Similar results were obtained for myrtle seed, black cumin and niger seed (Aidi Wannes and Marzouk 2016) considered as a common source of polyunsaturated linoleic acid.

A dietary intake of PUFA plays an important role on the regulation of lipid metabolism and the prevention of cardiovascular diseases (Müller et al. 2003). However, a high intake of SFA is associated with a high level of serum cholesterol (Müller et al. 2003). Thus, FAO (2001) reported that GSO consumption may be beneficial for human health with a balanced intake of dietary PUFA and SFA.

Fatty acids composition of canned sardine samples

The study enabled us to know the effect of canning process and coating-oil nature on the fatty acids profiles and lipids quality indicators of sardine flesh.

Table 4 summarized the fatty acids composition of the tested samples (Fs, GSOs and OOs).

Table 4.

Changes in fatty acids profile (%) of Sardina pilchardus flesh canned in grape seed and olive oils following 1 and 3 months of storage

	Fs	OOs, 1 month	OOs,3 months	GSOs, 1 month	GSOs, 3 months	SEM	Pr > F
C10:0	1.67 ± 0.05a	0.21 ± 0.01d	0.13 ± 0.01e	0.36 ± 0.05c	1.10 ± 0.01b	0.02	0.0001
C12:0	0.70 ± 0.02a	0.15 ± 0.02d	0.07 ± 0.00e	0.18 ± 0.02c	0.27 ± 0.00b	0.01	0.0001
C14:0	4.32 ± 0.19a	1.24 ± 0.11c	1.09 ± 0.01c	1.31 ± 0.19c	2.19 ± 0.01b	0.07	0.0001
C15:0	1.02 ± 0.05a	0.35 ± 0.03d	0.29 ± 0.01d	0.73 ± 0.05c	0.80 ± 0.01b	0.02	0.0001
C16:0	26.31 ± 0.94a	24.21 ± 0.06cb	20.24 ± 0.04d	23.66 ± 0.04c	24.54 ± 0.05b	0.24	0.0001
C17:0	0.49 ± 0.07b	1.6 ± 0.01a	0.12 ± 0.00d	0.19 ± 0.00c	0.15 ± 0.01 cd	0.02	0.0001
C18:0	6.03 ± 0.16a	4.13 ± 0.14b	3.18 ± 0.02d	3.02 ± 0.02d	3.85 ± 0.02c	0.05	0.0001
C20:0	0.22 ± 0.04a	0.21 ± 0.02a	0.10 ± 0.00b	0.10 ± 0.00b	0.10 ± 0.04b	0.01	0.0002
C22:0	0.10 ± 0.00d	0.2 ± 0.01c	0.30 ± 0.01b	0.45 ± 0.01a	0.21 ± 0.00c	0.00	0.0001
C14:1	0.20 ± 0.01a	0.18 ± 0.00b	0.10 ± 0.01d	0.12 ± 0.01c	0.10 ± 0.00d	0.00	0.0001
C15:1	0.36 ± 0.03a	0.20 ± 0.02c	0.03 ± 0.00d	0.18 ± 0.00c	0.30 ± 0.01b	0.01	0.0001
C16:1	2.64 ± 0.06a	2.00 ± 0.04b	1.82 ± 0.40bc	1.46 ± 0.06d	1.50 ± 0.01 cd	0.10	0.0001
C18:1	7.01 ± 0.22d	15.54 ± 0.07b	19.56 ± 0.01a	9.57 ± 0.22e	11.77 ± 0.02c	0.08	0.0001
C20:1	0.35 ± 0.02a	0.18 ± 0.01c	0.16 ± 0.01c	0.34 ± 0.02a	0.31 ± 0.01b	0.01	0.0001
C22:1	0.98 ± 0.02a	0.40 ± 0.02c	0.12 ± 0.02d	0.40 ± 0.02c	0.52 ± 0.02b	0.04	0.0001
C24:1	1.10 ± 0.03a	0.60 ± 0.03b	0.30 ± 0.03c	0.60 ± 0.03b	0.30 ± 0.05c	0.02	0.0001
C16:2	0.21 ± 0.02a	0.16 ± 0.01b	0.12 ± 0.01c	0.13 ± 0.02bc	0.11 ± 0.02c	0.01	0.0002
C16:3	0.19 ± 0.00a	0.12 ± 0.00d	0.09 ± 0.00e	0.17 ± 0.00b	0.16 ± 0.01c	0.00	0.0001
C16:4	0.1 ± 0.01a	0.01 ± 0.00b	0.10 ± 0.00a	0.10 ± 0.01a	0.10 ± 0.00a	0.00	0.0001
C18:2n-6	1.46 ± 0.05e	7.38 ± 0.03d	12.39 ± 0.09c	18.22 ± 0.06b	20.86 ± 0.06a	0.03	0.0001
C18:3n-3	1.09 ± 0.04a	0.10 ± 0.07d	0.50 ± 0.07c	0.90 ± 0.07b	0.20 ± 0.01d	0.03	0.0001
C18:4n-3	0.57 ± 0.02a	0.10 ± 0.01c	0.10 ± 0.01c	0.18 ± 0.01b	0.12 ± 0.02c	0.01	0.0001
C20:2n-6	1.22 ± 0.05a	0.40 ± 0.02d	0.50 ± 0.02c	0.40 ± 0.02d	0.60 ± 0.02b	0.02	0.0001
C20:3n-6	0.52 ± 0.01a	0.27 ± 0.00c	0.40 ± 0.00b	0.17 ± 0.00e	0.22 ± 0.01d	0.00	0.0001
C20:4n-6	4.38 ± 0.10c	3.26 ± 0.09d	5.59 ± 0.10a	4.57 ± 0.09b	2.51 ± 0.06e	0.05	0.0001
C20:3n-3	0.22 ± 0.01c	0.15 ± 0.01d	0.22 ± 0.00c	0.42 ± 0.01b	0.56 ± 0.02a	0.01	0.0001
C20:4n-3	1.12 ± 0.02a	0.30 ± 0.03d	0.60 ± 0.01c	0.59 ± 0.03c	0.66 ± 0.01b	0.01	0.0001
C20:5n-3 (EPA)	6.13 ± 0.19a	3.78 ± 0.08b	3.22 ± 0.01c	3.18 ± 0.02c	1.69 ± 0.15d	0.06	0.0001
C21:5	0.14 ± 0.01b	0.12 ± 0.01b	0.08 ± 0.02c	0.69 ± 0.02a	0.71 ± 0.02a	0.01	0.0001
C22:5n-6	0.52 ± 0.01c	0.36 ± 0.02d	0.09 ± 0.01e	0.61 ± 0.01b	0.89 ± 0.01a	0.01	0.0001
C22:5n-3	1.22 ± 0.03c	0.50 ± 0.05d	0.02 ± 0.00e	1.48 ± 0.00b	1.65 ± 0.00a	0.01	0.0001
C22:6n-3(DHA)	27.41 ± 1.01b	31.59 ± 1.70a	28.37 ± 0.43b	25.52 ± 0.43c	20.95 ± 0.30d	0.54	0.0001
SFA	40.86 ± 1.01a	32.30 ± 0.27b	25.52 ± 0.07d	30.00 ± 0.25c	33.21 ± 0.10b	0.42	< 0.0001
MUFA	12.64 ± 0.26d	19.10 ± 0.13b	22.09 ± 0.32a	12.67 ± 0.24d	14.80 ± 0.08c	0.19	< 0.0001
PUFA	46.50 ± 1.05c	48.60 ± 1.42c	52.39 ± 0.52b	57.33 ± 0.53a	51.99 ± 0.48b	0.75	< 0.0001
PUFA/SFA	1.14 ± 0.00e	1.50 ± 0.031d	2.05 ± 0.02a	1.91 ± 0.00b	1.57 ± 0.010c	0.04	< 0.0001
∑n6/∑n3	0.13 ± 0.00b	0.10 ± 0.00c	0.17 ± 0.00a	0.16 ± 0.00a	0.13 ± 0.00b	0.01	< 0.0001
AI	0.80 ± 0.00a	0.49 ± 0.01d	0.41 ± 0.00e	0.58 ± 0.00c	0.76 ± 0.01b	0.00	< 0.0001
TI	1.15 ± 0.01a	0.71 ± 0.01e	0.78 ± 0.00d	1.01 ± 0.00b	0.96 ± 0.00c	0.02	< 0.0001

Values are mean values of three replicates ± standard deviation; Means with the same letter within lines are not significantly different (p > 0.05);

Fs fresh sardine; GSOs canned sardine in grape seeds oil; OOs canned sardine in olive oil; SEM standard error of the mean; SFA saturated fatty acids; PUFA polyunsaturated fatty acids; EPA eicosapentaenoic acid; DHA docosahexaenoic acid, AI atherogenic index; TI thrombogenic index

Overall, changes in the fatty acids profile were similar to results found by

Selmi and Sadok (2007) for flesh samples of Sardina pilchardus canned in tomato sauce and stored for six months.

The fatty acid profile was dominated by PUFA for all the tested samples (PUFA/SFA > 1). This ratio increased from 1.45 in fresh sardine to more than 2 in canned sardine (GSOs and OOs). Similar results were observed for canned sardine in tomato sauce (Selmi and Sadok 2007).

Among SFA, palmitic acid (C16:0) and stearic acid (C18:0) were the most dominant (ranging from 3 to 27%) for both canned samples. In addition, all the determined SFA were significantly higher in fresh sardine, except C17:0 and C22:0 (p < 0.05). Therefore, the canning process and storage duration had significant effects on saturated fatty acids (the total SFA decreased from 40.86 to 25.52% and 33.22% respectively for OOs and GSOs). This was in accordance with results of Selmi and Sadok (2007) who reported that the canning process had significant effect on saturated fatty acids.

Table 4 shows that MUFA were also affected by the process and decreased significantly with storage duration after canning the sardine flesh (p < 0.05). However, the only MUFA which significantly increased after processing the raw fish was the oleic acid (C18:1) for both coating oils. It was the major MUFA and reached 19.56 ± 0.01% in OOs and 11.77 ± 0.02% in GSOs compared to 7.01 ± 0.22% in the fresh fish. Thus, total MUFA increased especially for OOs samples (from 12.64 ± 1.013% in FS to 22.09 ± 0.11%) (Table 4).

Furthermore, the major PUFA in all analyzed samples was Docosahexaenoic acid (DHA), which decreased significantly in GSOs, whereas, it increased in OOs samples to reach 31.59 ± 1.7%.

In fresh sardine, EPA was the second most abundant PUFA. However, in processed samples, linoleic acid (C18:2n6) was more abundant since it increased significantly to reach in 90 days: 20.86 ± 0.06% for GSOs and 12.39 ± 0.09% for OOs compared to 1.46 ± 0.05% for Fs (Table 4).

Overall, DHA was the most abundant unsaturated fatty acid, followed by linoleic acid in GSOs samples and oleic acid in OOs samples.

This is due to fatty acids composition of the coating oil. Indeed, as shown in Table 3, GSO was rich in linoleic acid (65%), while oleic acid is well-recognized to be the most important fatty acid in OO (> 60%) followed by linoleic acid (Selmi and Sadok 2007).

As expected, the canned sardine fatty acid profile was influenced by the coiting oil used. In fact, canning sardine with GSO added to the particular nutritional characteristics of the sardines (rich in omega 3: DHA and EPA) with the GSO benefits (high amount of linoleic acid). This coating oil, had diffused into fish tissue, reduced the percentages of EPA and DHA initially present in raw fish and substituted them with linoleic and oleic fatty acids. This is associated with the high nutritional value and oxidative stability of C18:2 n6 and C20:2 n6.

Similar results were obtained with samples of canned tuna and sardine (Selmi et al. 2008).

Over and above the high amounts of omega 3 (DHA, EPA) in fresh sardine, which have anti-inflammatory and neuroprotective properties (Dyall 2015), the abundance of linoleic acid in canned samples (GSOs) may help to prevent cardiovascular diseases, improve wound healing but also can counteract insulin resistance in obese women and this result represents hope for diabetes prevention (Irandoost et al. 2013).

Nutritional quality of lipids of canned sardine samples

The FAO/WHO and the United Kingdom Department of Health stipulated a maximum dietary ratio of ω6/ω3 of 4 and a minimum value of the PUFA/SFA ratio of 0.45 and considers higher ratios (> 0.2) more beneficial to human health (UKDH 1994).

In this study, canned sardine in both coating oils seems to have an interesting nutritional value since these ratios meet the recommended values (Table 4).

Moreover, to evaluate the susceptibility of ingested fat from marine foods to influence the risk associated with coronary heart disease, the atherogenic and thrombogenic indices were created by Ulbricht and Southgate (1991).

In fact, these indices indicate potential for stimulating platelet aggregation. In fact, atherogenic indices reflects the relationship between saturated and unsaturated FA or proatherogenic FA (favoring the adhesion of lipids to cells of the immunological and circulatory system), and anti-atherogenic FA (inhibiting the aggregation of plaque and decrease the levels of cholesterol and phospholipids); thus preventing the appearance of micro- and macro-coronary diseases. Moreover, thrombogenic indices shows tendency to form clots in the blood vessels (Ulbricht and Southgate 1991).

Therefore, atherogenic and thrombogenic indices must be lower than 1 to prevent heart diseases (Ulbricht and Southgate 1991). In this context, our results showed that the canning process in OO and GSO considerably decreased these two indices from 0.8 and 1.17 in fresh sardine to less than 1. Thus, the GSO had improved the nutritional quality of lipids in fresh sardine.

This was essentially due to the antioxidant capacity present in GSO which is directly related to high concentrations of PUFA namely EPA and DHA, phenolic acids, carotenoids, flavonoids and vitamine E rarely found in other oils (Bellili et al. 2018).

Thiobarbituric acid index and total volatile bases nitrogen

The susceptibility of fatty acids to oxidation is correlated with their PUFA contents. Fats with a high degree of unsaturation are more sensitive to oxidation (Gray, 1978). TBA and TVBN measurements were used to determine the extent of sardine oxidation after the canning process and during storage (Table 5).

Table 5.

Changes in total volatile base nitrogen (TVBN) and thiobarbituric acid index (TBA) of canned sardine in different oil medium and following 1, 2 and 3 months of storage

	TVBNi	TVBN1	TVBN2	TVBN3	TBAi	TBA1	TBA2	TBA3
GSOs	4.45 ± 0.05b	12.50 ± 0.02b	17.50 ± 0.05b	23.06 ± 0.05b	0.71 ± 0.05a	1.00 ± 0.02b	1.20 ± 0.05b	1.29 ± 0.03b
OOs	5.45 ± 0.04a	17.20 ± 0.02a	18.70 ± 0.04a	24.06 ± 0.03a	0.65 ± 0.04a	1.25 ± 0.02a	1.60 ± 0.04a	2.07 ± 0.05a
SEM	0.02	0.01	0.02	0.04	0.02	0.01	0.03	0.04
Pr > F	0.0001	0.0001	0.0001	0.0001	0.064	0.0001	0.0001	0.0001

Values are mean values of three replicates ± standard deviation; Means with the same letter within column are not significantly different (p > 0.05); Fs: fresh sardine

GSOs canned sardine in grape seed oil; OOs canned sardine in olive oil. SEM standard error of the mean; TVBN total volatile base nitrogen (mg N₂ 100 g⁻¹); TBA thiobarbituric acid index (mg malonaldehyde kg⁻¹); i: initial; 1,2,3: storage months

The chemical analysis revealed that TVBN and TBA of fresh sardine averaged respectively 3.23 ± 0.01 mg/100 g and 0.6 ± 0.21 mg malonaldehyde/ kg.

For both tested oils, TBA and TVBN in canned sardines increased in the first stage of the canning process but also after the storage period. TVBN increased from 4.45 mg/100 g and 5.45 mg/100 g to 23.06 mg/100 g and 24.06 mg/100 g respectively for GSO s and OOs. In fact, the increase in TVBN can be caused by the increase in ammonia liberated by the deamination of adenosine monophosphate or amino acids.

In addition, TBA reached 1.29 mg and 2.07 mg malonaldehyde/ kg for GSOs and OOs respectively (Table 5). This may be due to the highly unsaturated fatty acids present in samples of canned sardine. The results of this study were lower than that of Selmi et al. (2008) for canned sardine and tuna in tomato sauce and OO.

Nevertheless, levels of TVBN and TBA remained lower than the threshold limits during the processing and the storage period. Indeed, fish is considered to be of good quality if TBA value is less than or equal to 5 mg malonaldehyde /kg.

In addition, the Spanish Foreign Trade and Inspection Center suggested a limit of 80 mg/100 g for TVBN contents (Pons Sánchez-Cascado 2006). Levels of TVBN in all analyzed samples remained under this limit.

Moreover, for both analyzed parameters and during the storage, TBA and TVBN were significantly lower in GSOs than in OOs (p = 0.0001), except for initial values of TBA measured directly after sterilisation process. Therefore, GSO seems to have great benefit to prevent protein and lipid alteration. The potent antioxidant activity of GSO is due to the presence of bioactive compounds namely polyphenols and sterols. Those molecules are mostly known for their antioxidant properties (Harbeoui et al. 2018).

The study of Harbeoui et al. (2018) confirmed the strong chelating capacity and the high reducing power of grape seed oils extracted from Tunisian varieties which exceeded that of butylated hydroxytoluene (BHT). This is in accordance with our findings.

Conclusion

On the basis of these findings, the use of GSO is strongly advised as an innovative method for canning sardine fish which combines the benefits of the sardine and GSO which is particularly rich in polyphenols. So this could be an opportunity to provide the consumer with a high quality product and to improve the nutritive value of the human diet.

Furthermore, this may increase the producer income, since several new products may be created for human consumption but also for non-food industries. The use of GSO in several products may also become an environmental impact topic, added to the economic worldwide market.

Nevertheless, other analysis of the effect of the canning process on amino acids composition and thiobarbituric acid reactive substances may be beneficial to provide a comprehensive overview of the chemical impact of GSO on canned sardine.

Alternative preservation method such as packaging under modified atmospheres with added GSO or powdered grape seed may also be worth further investigation.

Abbreviations

BHT

Butylated hydroxytoluene

DHA

Docosahexaenoic acid

EPA

Eicosapentaenoic

FA

Fatty acids

Fs

Fresh sardine

GSO

Grape seed oil

MUFA

Monounsaturated fatty acids

OO

Olive oil

PUFA

Polyunsaturated fatty acid

SFA

Saturated fatty acids

TBA

Thiobarbituric acid

TFA

Total fatty acid

TVBN

Total volatile base nitrogen

Authors' contributions

NB, responsible for conceiving the idea, carried out the experiments and wrote the MS. WRB and SM supervised the work and edited the manuscript. SM carried out the experiments. MT and J-PQ edited and supervised the work and corrected the manuscript.

Funding

Not applicable.

Availability of data and material

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Conflict of interest

The authors declare that they have no conflict of interest.

Ethics approval

Not applicable.

Consent to participate

Not applicable.

Code availability

Not Applicable.