Physicochemical Properties of French Fries After Several Cycles of Frying with Moringa or Olive Oil ^†

Abstract

Moringa oleifera oil is characterized by its high content of oleic acid (ω9), very similar to olive oil. Moreover, it is rich in linolenic acid (ω3) and behenic acid, among other fatty acids. Furthermore, this plant has lower agronomic requirements, and it resists high temperatures. Given the current geopolitical and climatic situation, several commonly consumed oils have suffered a price increase, making them less affordable to the population. Therefore, the aim of this work was to compare the properties of French fries obtained with moringa oil or olive oil after several frying cycles, in addition to assessing their sensorial acceptance. Fried potatoes were characterized in terms of mass variation, moisture, water activity (a_w), and optical and mechanical properties. The results showed that the potatoes fried with moringa oil lost less weight during frying, which was linked to the evaporation of water during the frying stage combined with the gain of oil. However, in all cases, the a_w was similar. The color was not affected by the type of oil used, but luminosity was lower after the third frying cycle in the case of potatoes fried with moringa oil. Mechanical properties were not affected by the type of oil applied. Finally, at the sensory level, the judges evaluated all samples above 5 points, penalizing the attributes of the first-cycle moringa oil fries for being too low.

1. Introduction

Moringa oleifera is a plant that has demonstrated remarkable adaptability to adverse climatic conditions, making it a viable option for sustainable agriculture in the context of climate change. Originally from northern India, moringa has spread to various tropical and subtropical regions of the world, including Africa, Asia, and Latin America. Its ability to grow in poor soils and withstand long periods of drought positions it as a resilient plant of great value to communities vulnerable to the effects of climate change [1]. In this context, its introduction in the Mediterranean basin, where there is a notable increase in temperatures along with a precipitation deficit, could be an alternative to traditional crops.

Moringa seeds are especially valued for their high oil content, which represents approximately 40% of their gross weight. This oil is rich in unsaturated fatty acids, mainly oleic acid (omega 9), which gives it outstanding nutritional and medicinal properties [2]. In addition to its use in food, moringa oil is used in the cosmetic and pharmaceutical industries due to its antioxidant, anti-inflammatory, and emollient properties. Recent studies have shown that moringa oil can help protect the liver, improve cardiovascular health, and combat bacterial and fungal infections [3].

The global consumption of potatoes is significant, with over a billion people regularly including them in their diet, making potatoes the third most important food crop worldwide [4]. Among the various forms of potato consumption, fried potatoes, such as French fries and potato chips, are particularly popular. However, the frying process can significantly impact the quality of the oil used. Frying at high temperatures leads to the degradation of oil, resulting in the formation of harmful compounds and a decrease in nutritional quality [5]. Studies have shown that the type of oil used and the frying conditions can influence the extent of these changes, affecting both the sensory properties of the fried product and its health implications. For instance, oils with higher stability, such as those rich in monounsaturated fats, are less prone to oxidation and can maintain better quality during frying [6].

Therefore, this work aimed to compare the physicochemical properties of French fries obtained with moringa oil and olive oil after several frying cycles, in addition to assessing their sensory acceptance.

2. Materials and Methods

2.1. Raw Materials

Potatoes (Alegria variety, origin Spain, 50/80 mm CAT I caliber) and extra virgin olive oil (Hojiblanca variety) purchased in a local supermarket were used. Moringa oil was extracted from moringa pod seeds grown in an experimental plot at the Universitat Politècnica de València (UPV) with a screw press at 100 °C (GBT26883-2011) at the University Institute of Food Engineering-FoodUPV.

2.2. Frying of the Potatoes

The potatoes were fried with a potato-oil ratio of 1:1.5, introducing them into the pan (16 cm diameter) when the oils reached a temperature of 160 °C and frying them for 4 min. The oil was stored in glass containers in the dark for use in the following cycles. This process was carried out in the same way for the three frying cycles analyzed.

2.3. Analytical Determinations

All analytical determinations on the potatoes and the oils were carried out before and after the frying process, at least in triplicate. The potatoes were weighed on an analytical balance before and after frying, and the change in mass was expressed as a function of the initial mass. The water content of the raw and fried potatoes was obtained by the AOAC gravimetric method (930.15.) in a vacuum oven (Selecta Vaciotem, 4001489). The water activity (a_w) of raw and fried potatoes was analyzed by a dew point hygrometer (Decagon Devices Inc of AquaLab TDL). For the analysis of the color of French fries, a colorimeter (Minolta, model CM-3600d) was used to obtain the CIELab coordinates by sextuplicate, taking as reference the observer 10° and illuminator D65. In addition, the color differences (ΔE) to fresh potatoes were calculated using Equation (1):

$${\Delta \mathrm{E}}^{*}=\sqrt{{\left({\Delta \mathrm{a}}^{*}\right)}^2+{\left({\Delta \mathrm{b}}^{*}\right)}^2+{\left({\Delta \mathrm{L}}^{*}\right)}^2}$$

(1)

A cutting test was carried out on the potatoes with a probe (A/BS cutting blade according to AIB method) at a feed rate of 0.5 mm/s using a universal press (Texturometer TA-XTplus Texture Analyse Aname, Godalming, UK) and analyzing the force up to the breaking point and the area under the curve. The measurements were carried out in sextuplicate.

2.4. Sensory Analysis

An organoleptic analysis of 4 French fries was carried out according to the oil used (M: moringa and O: olive) and considering one (C1) or three (C3) frying cycles. Thus, the samples chosen for this analysis were MC1, OC1, MC3, and OC3, which were coded with three-digit random numbers. The tasting was carried out by presenting the freshly fried potatoes to 14 judges. The questionnaire was carried out using the SensesBit platform, which included hedonic scale questions (9-point) [7,8] related to appearance, color, aroma, texture, taste, and overall acceptability. In addition, a penalty analysis was performed to find out whether an attribute above or below the JAR penalized the overall acceptability score.

2.5. Statistical Analysis

Statgraphics CenturionXIX.64 was used for statistical analysis of the results. An ANOVA analysis of variance was performed using the LSD (Least Significant Difference) test at a significance level of 95% (p-value ≤ 0.05) to determined statistical significant differences.

3. Results and Discussion

3.1. Physicochemical Properties

Figure 1 shows the weight variation suffered by the potatoes in each of the frying cycles, where it is observed that potatoes fried in olive oil lose significantly more weight than those fried with moringa oil for all cycles. This weight loss is linked to water evaporation during the frying stage combined with oil gain [9].

Therefore, in Figure 2, both the moisture and water activity of the potatoes after frying are shown.

When moringa oil was used, no significant differences in water content were observed with respect to fresh potato in any of the frying cycles, which would indicate that weight loss would be related only to oil gain. However, in the potato fried with olive oil, there was a significant decrease in water content when oil from a second or third frying cycle was used. Therefore, and relating weight loss to the final water content of the product, frying with moringa oil would favor obtaining less fatty products.

3.2. Optical Properties

Figure 3A shows the lightness L* of the potatoes studied with respect to the raw potato as a function of the cycles.

As can be seen, the lightness values were similar between the potatoes fried with both oils, decreasing significantly throughout the frying cycles. As regards color variation (ΔE), in Figure 3B, the color difference is represented. Potatoes fried with both oils presented significant differences with respect to the raw potato, although these differences remained constant with frying cycles in potatoes fried with olive oil, while they increased significantly in potatoes fried in moringa oil.

On the other hand, Figure 3C shows the representation in the chromatic diagram of the a* and b* coordinates and their variation throughout the frying cycles. All values were in the first quadrant (green-yellow zone). There were no significant differences between the frying cycles of potatoes fried in olive oil, although when fried in moringa oil, the a* coordinate increased significantly with the frying cycle. The increase in the a* coordinate during frying is due to non-enzymatic browning reactions (Maillard reactions) that occur due to the presence of reducing sugars [10]. This result is in agreement with that obtained by Lalas et al. [11], who also observed an increase in the a* coordinate during several potato frying cycles.

3.3. Mechanical Properties

Table 1. Maximum force and Area under the curve to the potato cut-off point.

Sample	Maximum Force (Newtons)	Area Under the Curve (N·s)
Olive C1	5.7 ± 1.9 b	27 ± 10 b
Olive C2	3.3 ± 0.5 a	12.2 ± 2.3 a
Olive C3	4.8 ± 1.9 ab	27 ± 9 b
Moringa C1	3.8 ± 1.2 ab	14.6 ± 6.6 a
Moringa C2	6.12 ± 1.5 b	30 ± 8 b
Moringa C3	5.9 ± 1.7 b	29 ± 11 b

Equal letters in the same column indicate homogeneous ANOVA groups with a 95% significance level. C1,2,3: frying cycles. OC1, OC2, OC3: olive oil, frying cycle 1,2,3; MC1, MC2, MC3: Moringa oil, frying cycles 1,2,3.

shows both the maximum force applied to cut the potato and the area under the curve up to the same point.

In potatoes fried with moringa oil, there was an increase in the mechanical parameters evaluated with the frying cycle, whereas non a clear tendency was observed in samples with olive oil. However, the changes recorded were very slight, so the type of oil does not seem to condition the mechanical properties of the final product. Pedreschi et al. [9] obtained similar maximum force values for French fries. According to Segnini et al. [12], the maximum breaking force is proportional to moisture content. Thus, the maximum force tends to decrease when moisture increases. Moreover, in the texture of French fries, there is great variability due to the changes in moisture and the heterogeneous distribution of starch and other compounds that affect the structure of French fries after frying [10].

3.4. Sensory Analysis

Figure 4 shows the results of the sensory analysis obtained from the survey of the attributes analyzed on a hedonic scale, both for the olive oil and moringa chips, specifically for the first and third cycles of each oil.

As can be seen, all attributes were rated higher than 5 points. On the other hand, texture was the only attribute that showed significant differences, with the potato fried with moringa oil of first frying (MC1) being the worst rated. Figure 5 shows the penalty graph of the olive oil and moringa potato chips in which the overall acceptance is related to the percentage of tasters who considered that the intensity of any of the attributes was too high or too low. In coherence with the previous results, the low intensity of all attributes was penalized for MC1 potato. In the case of MC3, only the low intensity of color and flavor was penalized. Potato fries with olive oil did not register penalties when obtained with the first frying cycle while increasing the cycles penalized flavor and texture for being too low.

4. Conclusions

In this study, the properties of moringa oil French fries were evaluated in comparison to those fried in olive oil. During the frying process, moringa oil French fries lost less weight and water compared to olive oil-fried chips. This suggests a reduced oil uptake and, consequently, lower caloric content. Moringa oil French fries were well-received in terms of flavor and texture. Tasters highlighted their pleasant taste and crispiness, indicating that the incorporation of moringa oil did not negatively impact the sensory experience. As frying cycles increased, moringa oil French fries developed a more intense flavor. This effect could be beneficial for products requiring a pronounced flavor profile. However, it is important to note that, compared to olive oil-fried potatoes, moringa-fried potatoes exhibited a less intense taste and aroma. This could influence consumer preference and should be considered in product design. In summary, moringa oil French fries offer a promising alternative from both a nutritional and sensory standpoint. Their lower caloric content and positive acceptance could make them an attractive option for health-conscious consumers. Nevertheless, further research is needed to fully understand their impact on final product quality.