Stability of avocado oil during heating: comparative study to olive oil

The stability of the saponifiable and unsaponifiable fractions of avocado oil, under a drastic heating treatment, was studied and compared to that of olive oil. Avocado and olive oil were characterised and compared at time 0 h and after different times of heating process (180 °C). PUFA/SFA (0.61 at t = 0) and ω-6/ω-3 (14.05 at t = 0) were higher in avocado oil than in olive oil during the whole experiment. Avocado oil was richer than olive oil in total phytosterols at time 0 h (339.64; 228.27 mg/100 g) and at 9 h (270.44; 210.30 mg/100 g) of heating. TBARs was higher in olive oil after 3 h, reaching the maximum values in both oils at 6 h of heating treatment. Vitamin E was higher in olive oil (35.52 vs. 24.5 mg/100 g) and it disappeared earlier in avocado oil (at 4 vs. 5 h). The stability of avocado oil was similar to that of olive oil

Unsaturated lipid matrices protect plant sterols from degradation during heating treatment

The interest in plant sterols enriched foods has recently enhanced due to their healthy properties. The influence of the unsaturation degree of different fatty acids methyl esters (FAME: stearate, oleate, linoletate and linolenate) on a mixture of three plant sterols (PS: campesterol, stigmasterol and β-sitosterol) was evaluated at 180 °C for up to 180 min. Sterols degraded slower in the presence of unsaturated FAME. Both PS and FAME degradation fit a first order kinetic model (R2 > 0.9). Maximum oxysterols concentrations were achieved at 20 min in neat PS and 120 min in lipid mixtures and this maximum amount decreased with increasing their unsaturation degree. In conclusion, the presence of FAME delayed PS degradation and postponed oxysterols formation. This protective effect was further promoted by increasing the unsaturation degree of FAME. This evidence could help industries to optimize the formulation of sterol-enriched products, so that they could maintain their healthy properties during cooking or processing

A review of analytical methods measuring lipid oxidation status in foods: a challenging task

Lipid oxidation analysis in food samples is a relevant topic since compounds generated in the process are related to undesirable sensory and biological effects. As the process is complex and depends on the type of lipid substrate, oxidation agents and environmental factors, proper measurement of lipid oxidation remains a challenging task. A great variety of methodologies have been developed and implemented so far, both for determining primary oxidation products and secondary oxidation products. Most common methods and classical procedures are described, including peroxide value, TBARS analysis and chromatography. Some other methodologies such as chemiluminescence, fluorescence emission, Raman spectroscopy, infrared spectroscopy or magnetic resonance, provide interesting and promising results, so attention must be paid to these alternative techniques in the area of food lipid oxidation analysis

Oxysterols formation: a review of a multifactorial process

Abstract Dietary sterols are nutritionally interesting compounds which can suffer oxidation reactions. In the case of plant sterols, they are being widely used for food enrichment due to their hypocholesterolemic properties. Besides, cholesterol and plant sterols oxidation products are associated with the development of cardiovascular and neurodegenerative diseases, among others. Therefore, the evaluation of the particular factors affecting sterol degradation and oxysterols formation in foods is of major importance. The present work summarizes the main results obtained in experiments which aimed to study four aspects in this context: the effect of the heating treatment, the unsaturation degree of the surrounding lipids, the presence of antioxidants on sterols degradation, and at last, oxides formation. The use of model systems allowed the isolation of some of these effects resulting in more accurate data. Thus, these results could be applied in real conditions

Sterols heating: Degradation and formation of their ring-structure polar oxidation products

Cholesterol and phytosterols can be oxidised under heating conditions to give sterol oxidation products (SOPs), known by their toxic effects. This paper studied the degradation of cholesterol and three plant sterols during a 360min heating treatment (180°C). The formation and further degradation of SOPs was also analysed by GC-MS. Results revealed a sterol susceptibility to degradation according to the following decreasing order: campesterol≈β-sitosterol⩾stigmasterol>cholesterol. The degradation curve fit (R(2)=0.907-0.979) a logarithmic model. SOPs increased their concentration during the first 5-10min and thereafter, their degradation rate was higher than their formation rate, resulting in a decrease over time. Irrespective of the sterol from which they had derived, 7-keto derivatives presented the highest levels throughout the entire process, and also SOPs with the same type of oxidation followed a similar degradation pattern (R=0.90-0.99)

Cholesterol and stigmasterol within a sunflower oil matrix: Thermal degradation and oxysterols formation

The characteristics of the lipid matrix surrounding sterols exert a great influence in their thermal oxidation process. The objective of this work was to assess the oxidation susceptibility of equal amounts of cholesterol and stigmasterol within a sunflower oil lipid matrix (ratio 1:1:200) during heating (180 ºC, 0 to 180 min). Remaining percentage of sterols was determined and seven sterol oxidation products (SOPs) were analyzed for each type of sterol along the heating treatment. Evolution of the fatty acid profile and vitamin E content of the oil was also studied. Overall oxidation status of the model system was assessed by means of Peroxide Value (PV) and TBARS. PV remained constant from 30 min onwards and TBARS continued increasing along the whole heating treatment. Degradation of both cholesterol and stigmasterol fitted a first order curve (R2= 0.937 and 0.883, respectively), with very similar degradation constants (0.004 min-1 and 0.005 min-1, respectively). However, higher concentrations of oxidation products were found from cholesterol (79 μg/mg) than from stigmasterol (53 μg/mg) at the end of the heating treatment. Profile of individual oxidation products was similar for both sterols, except for the fact that no 25-hydroxystigmasterol was detected. 7α-hydroxy and 7-ketoderivatives were the most abundant SOPs at the end of the treatment. PUFA and vitamin E suffered a significant degradation along the process, which was correlated to sterols oxidation

Solanum sessiliflorum (mana-cubiu) antioxidant protective effect towards cholesterol oxidation: influence of docosahexaenoic acid

Harmful health effects have been attributed to cholesterol oxidation products (COPs). Factors that modulate their formation in foods are light, oxygen, heat, and food matrix (such as antioxidants content or unsaturation degree of lipids), among others. The objective of this work was to assess the effectiveness of an extract obtained from Solanum sessiliflorum (mana‐cubiu) (MCE) as a potential inhibitor of cholesterol oxidation under heating conditions. The influence of free DHA presence in the system was also evaluated. Results showed that MCE inhibited cholesterol degradation (44 vs. 18% without and with MCE, respectively) and reduced ninefold COPs formation in the absence of DHA. However, when DHA was present, the MCE was not effective toward cholesterol oxidation. In this case, MCE showed its antioxidant effect protecting DHA from degradation (89 vs. 64%)

Role of Melissa officinalis in cholesterol oxidation: Antioxidant effect in model systems and application in beef patties

Cholesterol oxidation products (COPs) constitute a known health risk factor. The antioxidant effect of a lyophilized aqueous Melissa officinalis extract against cholesterol degradation and COPs formation during a heating treatment was evaluated in a model system (180 °C, 0–180 min) at a ratio of 2 mg extract/100 mg cholesterol. Furthermore, the plant extract was subsequently added to beef patties alone or incorporated within an oil-in-water olive oil emulsion to assess its effectiveness during cooking. Melisa extract protected cholesterol from thermal degradation in the model system, yielding higher remaining cholesterol and lower COPs values throughout the whole heating process. Maximum total COPs were achieved after 30 and 120 min of heating for control and melisa-containing samples, respectively. In cooked beef patties, even though the olive oil emulsion was used as flavor-masking approach, melisa extract off-flavor limited the maximum dose which could be added. At these doses (65 μg/g and 150 μg/g without and with the emulsion, respectively), no additional protective effect of melisa over the use of the emulsion was found. Addition of natural extracts into functional foods should definitively take into account sensory aspects

Thermo-oxidation of cholesterol: effect of the unsaturation degree of the lipid matrix

The influence of the unsaturation degree of different triacylglycerols (tristearin, triolein, trilinolein and trilinolenin) on cholesterol oxidation at 180 °C, was evaluated. Cholesterol degraded faster when heated alone than in the presence of triacylglycerols; moreover, the more unsaturated the matrix, the slower the degradation of cholesterol. Both cholesterol and triacylglycerols degradation fit a first order kinetic model (R(2)>0.9), except for the tristearin sample. Cholesterol oxidation products (COPs) and peroxides were formed during the heating treatment. The presence of any type of lipid matrix postponed and decreased the maximum concentration of both oxidation parameters. Maximum total COPs concentrations were achieved at 20 min in neat cholesterol, 120 min in tristearin and triolein and 180 min in polyunsaturated matrix samples. 7-Ketocholesterol was the main COP in most cases during the whole heating treatment. Both the presence of triacylglycerols and their unsaturation degree inhibited cholesterol thermooxidation at 180 °C