Investigations into acrylamide precursors in sterilized table olives: Evidence of a peptic fraction being responsible for acrylamide formation

Potassium Hydroxide Extraction of Polyphenols from Olive Leaves: Effect on Color and Acrylamide Formation in Black Ripe Olives

Olive leaves are generated in large quantities in olive oil and table olive factories. This waste is currently used for multiple purposes, one of them being the extraction of bioactive substances, in particular phenolic compounds. The aims of this study were (i) to obtain a new polyphenolic extract from potassium hydroxide (KOH) -treated olive leaves; and (ii) to reduce acrylamide formation in black olives by using this extract. The results showed that olive leaves and leafless branches of the Manzanilla cultivar treated with 10 g/L KOH provide a solution that, concentrated under vacuum, had >6000 mg/L hydroxytyrosol and >2000 mg/L of hydroxytyrosol 4-glucoside. Moreover, the residual material generated after the treatment with KOH could be used for agronomic purposes, due to its high potassium content. The employment of this non-bitter extract during the darkening step of black ripe olive processing then resulted in darker fruits with higher potassium content. Likewise, the addition of the extract into the packing brine reduced the acrylamide formation by up to 32%, although this effect was batch-dependent. KOH olive extract could be useful for the reduction in acrylamide in black ripe olives along with the enrichment of this product in phenolic compounds and potassium.

Effect of elaboration process, crop year and irrigation on acrylamide levels of potential table olive varieties

BACKGROUND

Table olives are widely consumed in the Mediterranean diet, and several typical Spanish and Portuguese varieties could potentially be used as such. In order to ensure a good-quality product, the effect of different factors such as elaboration processes, irrigation conditions, crop year and their crossover interaction on acrylamide content and antioxidant compounds needs to be deeply studied.

RESULTS

When looking through irrigation, regulated deficit irrigation (RDI) presented lower acrylamide levels than rainfed conditions for 'Cordovil de Elvas', 'Picual' and 'Verdeal Alentejana'. No significant interactions were found between the type of irrigation and elaboration style for 'Arbequina' and 'Koroneiki' varieties. Although RDI had the largest concentration of total phenols, antioxidant activity was also the highest. The table olives harvested in the crop year of 2019 showed lower levels of acrylamide due to a significant relationship between the crop year and irrigation conditions.

CONCLUSIONS

Novel varieties to be marketed should be taken into consideration for table olive elaboration. The impact of the crop year on the bioactive value of table olives and crossover interactions relies strongly in climatological conditions. Last but not least, the benefit of selecting the best irrigation and elaboration methods is crucial to ensure desirable acrylamide levels. © 2023 Society of Chemical Industry.

Heat-Introduced Formation of Acrylamide in Table Olives: Analysis of Acrylamide, Free Asparagine, and 3-Aminopropionamide

Acrylamide was detected in considerable amounts in black table olives. In this study, besides black, also green and naturally black table olives were investigated for their acrylamide, free asparagine, and 3-aminopropionamide contents before and after heat treatment. Acrylamide amount was 208-773 μg/kg in black table olives and did not change due to heat treatment. In green and naturally black table olives acrylamide was ≤24 μg/kg before heat treatment and rose to 1200 μg/kg afterward. Asparagine content was 0.35-35 mg/kg in all samples before heat treatment and after heat treatment with no considerable change in the range. 3-Aminopropionamide showed amounts of ≤56 μg/kg in the unheated samples and increased up to 131 μg/kg due to heat impact. However, quantified asparagine and 3-aminopropionamide amounts were insufficient in almost all samples to explain the acrylamide quantities formed due to heat treatment based on the formation via the Maillard reaction.

Characterization of Polyphenol and Volatile Fractions of Californian-Style Black Olives and Innovative Application of E-nose for Acrylamide Determination

Californian-style black olives require a sterilization treatment that produces a carcinogenic contaminant, acrylamide. Thus, this compound was evaluated in two different olive cultivars using an electronic nose (E-nose). The sterilization intensity had a significant influence on the final phenol concentrations, acrylamide content, and volatile compounds. Increasing the sterilization intensity from 10 to 26 min (F0) reduced the phenol content, but it promoted acrylamide synthesis, leading to a wide range of this toxic substance. The Ester and phenol groups of volatile compounds decreased their content when the sterilization treatment increased; however, aldehyde and other volatile compound groups significantly increased their contents according to the thermal treatments. The compounds 4-ethenyl-pyridine, benzaldehyde, and 2,4-dimethyl-hexane are volatile compounds with unpleasant odours and demonstrated a high amount of influence on the differences found after the application of the thermal treatments. The “Manzanilla Cacereña” variety presented the highest amount of phenolic compounds and the lowest acrylamide content. Finally, it was found that acrylamide content is correlated with volatile compounds, which was determined using multiple linear regression analysis (R² = 0.9994). Furthermore, the aroma of table olives was analysed using an E-nose, and these results combined with Partial Least Square (PLS) were shown to be an accurate method (range to error ratio (RER) >10 and ratio of performance to deviation (RPD) >2.5) for the indirect quantification of this toxic substance.

Industrial Strategies to Reduce Acrylamide Formation in Californian-Style Green Ripe Olives

Acrylamide, a compound identified as a probable carcinogen, is generated during the sterilization phase employed during the processing of Californian-style green ripe olives. It is possible to reduce the content of this toxic compound by applying different strategies during the processing of green ripe olives. The influence of different processing conditions on acrylamide content was studied in three olives varieties (“Manzanilla de Sevilla”, “Hojiblanca”, and “Manzanilla Cacereña”). Olives harvested during the yellow–green stage presented higher acrylamide concentrations than green olives. A significant reduction in acrylamide content was observed when olives were washed with water at 25 °C for 45 min (25% reduction) and for 2 h (45% reduction) prior to lye treatment. Stone olives had 21–26% higher acrylamide levels than pitted olives and 42–50% higher levels than sliced olives in the three studied varieties. When calcium chloride (CaCl₂) was added to the brine and brine sodium chloride (NaCl) increased from 2% to 4%, olives presented higher concentrations of this contaminant. The addition of additives did not affect acrylamide levels when olives were canned without brine. Results from this study are very useful for the table olive industry to identify critical points in the production of Californian-style green ripe olives, thus, helping to control acrylamide formation in this foodstuff.

Comparative Study of Four Analytical Methods for the Routine Determination of Acrylamide in Black Ripe Olives

Reducing acrylamide in foods is an important scientific and regulatory goal. Black ripe olives contain significant levels of acrylamide. However, unlike cereal and potato products, there are no standardized methods or certified reference materials for olives and no harmonization between laboratories performing routine analyses. The industry has observed inconsistencies between laboratories using different analytical methods. To narrow the cause of this variability, acrylamide was extracted from olives using a single protocol and analyzed with the most commonly used routine methods: liquid chromatography with ultraviolet detection (LC-UV) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) without bromination and LC-UV and gas chromatography-mass spectrometry (GC-MS) following bromination. This design specifically evaluated the effects of sample derivatization and detector on acrylamide measurements, which has not been documented for any food. Accuracy, precision, sensitivity, linearity, and reproducibility were assessed, and 10 commercial olive samples were analyzed. LC-MS/MS demonstrated the best overall performance. Although derivatization decreased precision and reproducibility, all detection methods had comparable accuracy and calculated acrylamide values. The results suggest that harmonization of extraction protocols across laboratories is the most important area of future study. This study provides the framework for a standardized method for acrylamide analysis in olives. Reliable measurements are essential for aiding the decision making of the industry and regulatory agencies.

Reducing Phenolics Related to Bitterness in Table Olives

Olives are one of the oldest food products in human civilization. Over the centuries, numerous methods have been developed to transform olives from a bitter drupe into an edible fruit. Methods of processing table olives rely on the acid, base, and/or enzymatic hydrolysis of bitter phenolic compounds naturally present in the fruit into nonbitter hydrolysis products. Today, there are three primary methods of commercial table olive processing: the Greek, Spanish, and Californian methods, in addition to several Artisanal methods. This review focuses on the technological, microbiological, chemical, and sensory aspects of table olive processing and the inherent benefits and drawbacks of each method. The table olive industry is facing challenges of environmental sustainability and increased consumer demand for healthier products. Herein, we examine current research on novel technologies that aim to address these issues.

Acrylamide: inhibition of formation in processed food and mitigation of toxicity in cells, animals, and humans

Potentially toxic acrylamide is largely derived from the heat-inducing reactions between the amino group of the amino acid asparagine and carbonyl groups of glucose and fructose in plant-derived foods including cereals, coffees, almonds, olives, potatoes, and sweet potatoes. This review surveys and consolidates the following dietary aspects of acrylamide: distribution in food, exposure and consumption by diverse populations, reduction of the content in different food categories, and mitigation of adverse in vivo effects. Methods to reduce acrylamide levels include selecting commercial food with a low acrylamide content, selecting cereal and potato varieties with low levels of asparagine and reducing sugars, selecting processing conditions that minimize acrylamide formation, adding food-compatible compounds and plant extracts to food formulations before processing that inhibit acrylamide formation during processing of cereal products, coffees, teas, olives, almonds, and potato products, and reducing multiorgan toxicity (antifertility, carcinogenicity, neurotoxicity, teratogenicity). The herein described observations and recommendations are of scientific interest for food chemistry, pharmacology, and toxicology, but also have the potential to benefit nutrition, food safety, and human health.

Influence of California-style black ripe olive processing on the formation of acrylamide

Methods used in processing California-style black ripe olives generate acrylamide. California-style black ripe olives contain higher levels of acrylamide (409.67 ± 42.60-511.91 ± 34.08 μg kg(-1)) as compared to California-style green ripe olives (44.02 ± 3.55-105.79 ± 22.01 μg kg(-1)), Greek olives (<1.42 μg kg(-1)), and Spanish olives (not detected), indicating that the higher temperatures used to sterilize the California-style green ripe and black ripe olives are required for acrylamide formation. Preprocessing brine storage influenced the formation of acrylamide in a time-dependent manner. Acrylamide increased during the first 30 days of storage. Longer brine storage times (>30 days) result in lower acrylamide levels in the finished product. The presence of calcium ions in the preprocessing brining solution results in higher levels of acrylamide in finished products. Air oxidation during lye processing and the neutralization of olives prior to sterilization significantly increase the formation of acrylamide in the finished products. Conversely, lye-processing decreases the levels of acrylamide in the final product. These results indicate that specific steps in the California-style black ripe olive processing may be manipulated to mitigate the formation of acrylamide in finished products.