Physico-Chemical, Microbiological and Sensory Evaluation of Ready-to-Use Vegetable Pâté Added with Olive Leaf Extract

Formulation development and characterization of plant-based alternatives to pâté using forest ingredients

Due to the expanding global population and environmental concerns about meat production from livestock, there is a great demand for alternative ingredients. Beech achene (BA) and sessile oak acorn (SOA) were recently proposed as protein- and carbohydrate-rich novel food ingredients. This study used their roasted kernels to develop and characterize four formulations of spreadable vegetable paste (with 10% BAK, 10% SOAK, 5% SOAK + 5% BAK, and control-just with roasted sunflower kernel). The substitution of sunflower kernel with 10% BAK caused a decrease in the energy value of vegetable paste, while 10% SOAK and 5% SOAK + 5% BAK, an increase. Syneresis was higher in formulations with forest ingredients, most notably in those containing BAK. The SOAK also caused a decrease in the pH of vegetable pastes that included it. All forest formulations had a large total colour difference compared to the control sample, driven by its intensity decrease (less in that with BAK than in the other two). The acceptance rate was reasonable for all formulations, although the overall score was significantly lower (slightly liked) in the vegetable paste formulated only with BAK than in the others (moderately liked); thus, the consumer's purchase intention too (only 4.9% for that with 10% SOAK). Formulation with 10% BAK had a higher hardness, adhesiveness, gumminess, and chewiness than the others, while that with the 5% SOAK and 5% BAK mixture showed the most robust network structure. In conclusion, BA and SOA kernels are suitable for manufacturing plant-based alternatives to pâté if used in proper concentrations.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05852-7.

White rice enrichment with phenols upon cooking in olive leaf infusion: a preliminary study

BACKGROUND

White rice is poor in health-promoting phytochemicals; therefore, the production of a phenol-enriched commodity is highly desirable. Recent findings on its enrichment via cooking in plant extracts are promising, yet studies employing aqueous extracts of olive leaves (OLs), containing well-recognized bioactive phenols (e.g. oleuropein) are absent. In addition, little is known about the levels of phenols that are maintained after rice drying and rehydration, an important aspect for the future design of 'ready-to-eat' functional rice.

RESULTS

The examination, for the first time, of white rice adsorption capacity of phenols from OLs upon cooking in infusions containing different levels of phenols, after freeze-drying and rehydration, showed the following: (i) the total phenol content, the antioxidant activity (assessed via 2,2-diphenyl-1-picrylhydrazyl radical and ferric reducing antioxidant power assays), the oleuropein and luteolin-7-O-glucoside levels increased dose dependently; (ii) upon rehydration, the average decrease of total phenol content and antioxidant activity values was significantly lower when an exact volume of water was used compared with an excess (~10% versus 63%). A similar trend was observed for oleuropein (36% versus 83%) and the luteolin-7-O-glucoside (24 versus 82%) levels; (iii) the dried enriched kernels were less bright with a hay-yellow hue (CIELab coordinates).

CONCLUSION

White rice enrichment with biophenols from OLs, a by-product of olive tree cultivation, was successful using a simple approach. Despite leaching upon freeze-drying/rehydration, sufficient amounts were maintained to obtain a functional rice that could serve as an alternative dietary source of OLs phenols to non-traditional olive tree product consumers or those refraining from sodium and fats. © 2023 Society of Chemical Industry.

Valorizing the usage of olive leaves, bioactive compounds, biological activities, and food applications: A comprehensive review

Olive oil production is a significant source of economic profit for Mediterranean nations, accounting for around 98 percent of global output. Olive oil usage has increased dramatically in recent years, owing to its organoleptic characteristics and rising knowledge of its health advantages. The culture of olive trees and the manufacture of industrial and table olive oil produces enormous volumes of solid waste and dark liquid effluents, involving olive leaves, pomace, and olive oil mill wastewaters. These by-products cause an economic issue for manufacturers and pose major environmental concerns. As a result, partial reuse, like other agronomical production wastes, is a goal to be achieved. Because these by-products are high in bioactive chemicals, which, if isolated, might denote components with significant added value for the food, cosmetic, and nutraceutical sectors, indeed, they include significant amounts of beneficial organic acids, carbohydrates, proteins, fibers, and phenolic materials, which are distributed differently between the various wastes depending on the olive oil production method and table olive agronomical techniques. However, the extraction and recovery of bioactive materials from chosen by-products is a significant problem of their reasonable value, and rigorous detection and quantification are required. The primary aims of this review in this context are to outline the vital bioactive chemicals in olive by-products, evaluate the main developments in extraction, purification, and identification, and study their uses in food packaging systems and safety problems.

Comparative Physicochemical, Microbiological, Antioxidant, and Sensory properties of pre- and post-fermented yoghurt enriched with olive leaf and its extract

This study investigated the comparative effect of yoghurt samples enriched with different concentrations of olive leaf powder (OLP) (0.1, 0.5, 1, and 1.5 mg/ml) and its extract (OLE) (0.5, 1, 3, and 5 mg/ml) on the microbiological, sensory, physicochemical, and antioxidant properties of pre‐ and post‐fermented samples during 21 days of storage. Sensory evaluation showed that concentrations lower than 1.5 and 5 mg/ml of OLP and OLE, respectively, were acceptable. Adding OLP or OLE did not have an influence on yoghurt starter culture bacteria (p > .05). All enriched samples significantly showed higher acidity and lower pH compared with control samples (p < .05). The most important polyphenols were oleuropein (from 0.132 to 0.224 and 0.373 to 0.413 mg/g for 0.5 and 3 mg/ml of OLE, from 0.194 to 0.321 mg/g and 0.413 to 1.280 mg/g for 0.5 and 1 mg/ml of OLP, respectively) and catechin (from 0.369 to 0.382 and 0.461 to 0.477 mg/g for 0.5 and 3 mg/ml of OLE, from 0.386 to 0.405 mg/g and 0.310 to 0.710 mg/g for 0.5 and 1 mg/ml of OLP, respectively) in enriched yoghurts. Adding OLP or OLE increased shelf life, antioxidant activity percentage (AA%), and total phenol content (TPC) of enriched samples (p < .05). During 21 days of storage of all samples, TPC, AA%, and pH decreased and TTA increased.

State-of-Art on the Recycling of By-Products from Fruits and Vegetables of Mediterranean Countries to Prolong Food Shelf Life

Annually, 1.3 billion tons of food are wasted and this plays a major role in increasing pollution. Food waste increases domestic greenhouse gas emissions mainly due to the gas emissions associated with its production. Fruit and vegetable industrial by-products occur in the form of leaves, peel, seeds, pulp, as well as a mixture of them and represent the most abundant food waste. The disposal of agricultural by-products costs a large amount of money under certain governmental regulations. However, fruit and vegetable by-products are rich in valuable bioactive compounds, thus justifying their use as food fortifier, active food packaging or as food ingredients to preserve food quality over time. The present review collects the most recent utilization carried out at lab-scale on Mediterranean fruit and vegetable by-products as valid components to prolong food shelf life, providing a detailed picture of the state-of-art of literature on the topic. Bibliographic research was conducted by applying many keywords and filters in the last 10 years. Several scientific findings demonstrate that by-products, and in particular their extracts, are effectively capable of prolonging the shelf life of dairy food, fresh-cut produce, meat and fish-based products, oil, wine, paste and bakery products. All of the studies provide clear advances in terms of food sustainability, highlight the potential of by-products as a source of bioactive compounds, and promote a culture in which foods are intended to receive a second useful life. The same final considerations were also included regarding the current situation, which still limits by-products diffusion. In addition, a conclusion on a future perspective for by-products recycling was provided. The most important efforts have to be conducted by research since only a multidisciplinary approach for an advantageous investigation could be an efficient method to promote the scale up of by-products and encourage their adoption at the industrial level.

Nutritional Improvement of Gluten-Free Breadsticks by Olive Cake Addition and Sourdough Fermentation: How Texture, Sensory, and Aromatic Profile Were Affected?

There is a growing need for gluten-free bakery products with an improved nutritional profile. Currently, gluten-free baked goods deliver low protein, fiber, and mineral content and elevated predicted glycaemic index (pGI). Olive cake (OC), a by-product from virgin olive oil extraction, is an excellent natural source of unsaturated fatty acids, dietary fiber and bioactive molecules, including polyphenols and tocopherols. In this framework, this study aimed at using two selected lactic acid bacteria and a yeast for increasing the antioxidant features and the phenol profile of the gluten-free breadsticks fortified with OC with the perspective of producing a functional food. Control (CTR) samples were prepared and compared with fermented ones (fCTR). Samples were added with either non-fermented OC (nfOC) or fermented for 12 and 20 h (fOC-12 and fOC-20). Our results showed that the predicted glycemic index (pGI) was influenced by both OC addition and sourdough fermentation. In fact, the lowest value of pGI was found in fOC-12, and hydrolysis index and pGI values of samples with OC (fOC-12 and nfOC) were statistically lower than fCTR. Both OC addition and fermentation improved the total phenol content and antioxidant activity of breadsticks. The most pronounced increase in hardness values was observed in the samples subjected to sourdough fermentation as evidenced both from texture profile analysis and sensory evaluation. Moreover, in most cases, the concentration of the detected volatile compounds was reduced by fermentation. Our work highlights the potential of OC to be upcycled in combination with fermentation to produce gluten-free breadsticks with improved nutritional profile, although additional trials are required to enhance textural and sensory profile.

Olive Leaf Extract (OLE) Addition as Tool to Reduce Nitrate and Nitrite in Ripened Sausages

Olive leaf extract (OLE) is known to be a source of phenolic compounds with antioxidant and antimicrobial activities. This study investigated the effects of the OLE addition to reduce nitrate/nitrite (NO) content on the physico-chemical features of ripened pork sausages. Seven formulations of pork sausages were set up: CTRL (0 mg/kg OLE; 300 mg/kg NO), Tr1 (200 mg/kg OLE; 150 mg/kg NO), Tr2 (400 mg/kg OLE; 150 mg/kg NO), Tr3 (800 mg/kg OLE; 150 mg/kg NO), Tr4 (200 mg/kg OLE; 0 mg/kg NO), Tr5 (400 mg/kg OLE; 0 mg/kg NO), and Tr6 (800 mg/kg OLE; 0 mg/kg NO). At the end of the ripening period, all the samples were within hygienic limits and the substitution of the additives with OLE allowed the reduction of NO residual contents. Both OLE and NO influenced the colour parameters. At the highest dose of OLE, both alone and in combination with reduced dose of NO, no significant differences in terms of moisture, pH, and aw were found compared to CTRL. In absence of NO, a significant reduction of weight loss was observed. Moreover, in the samples without NO a reduction of the hardness was detected. Finally, the oxidative stability test showed that the increase of the OLE amount prolonged the induction time.

Logistic modeling to predict the minimum inhibitory concentration (MIC) of olive leaf extract (OLE) against Listeria monocytogenes

Olive leaf extract (OLE) has been increasingly recognized as a natural and effective antimicrobial against a host of foodborne pathogens. This study attempts to predict the minimum inhibitory concentration (MIC) of OLE against Listeria monocytogenes F2365 by utilizing the asymptotic deceleration point (PDA) in a logistic model (LM), namely MIC-PDA. The experimental data obtained from the inhibitory rate (IR) versus OLE concentration against L. monocytogenes were sufficiently fitted (R2 = 0.88957). Five significant critical points were derived by taking the multi-order derivatives of the LM function: the inflection point (PI), the maximum acceleration point (PAM), the maximum deceleration point (PDM), the absolute acceleration point (PAA), and the asymptotic deceleration point (PDA). The PDA ([OLE] = 37.055 mg/mL) was employed to approximate the MIC-PDA. This MIC value was decreased by over 42% compared to the experimental MIC of 64.0 mg/mL, obtained using the conventional 2-fold dilution method (i.e., MIC-2fold). The accuracy of MIC-PDA was evaluated by an in vitro L. monocytogenes growth inhibition assay. Finally, the logistic modeling method was independently validated using our previously published inhibition data of OLE against the growths of Escherichia coli O157:H7 and Salmonella enteritidis. The MIC-PDA (for [OLE]) values were estimated to be 41.083 and 35.313 mg/mL, respectively, compared to the experimental value of 62.5 mg/mL. Taken together, MIC-PDA, as estimated from the logistic modeling, holds the potential to shorten the time and reduce cost when OLE is used as an antimicrobial in the food industry.

Phenolic-Rich Plant Extracts With Antimicrobial Activity: An Alternative to Food Preservatives and Biocides?

In recent years, the search for natural plant-based antimicrobial compounds as alternatives to some synthetic food preservatives or biocides has been stimulated by sanitary, environmental, regulatory, and marketing concerns. In this context, besides their established antioxidant activity, the antimicrobial activity of many plant phenolics deserved increased attention. Indeed, industries processing agricultural plants generate considerable quantities of phenolic-rich products and by-products, which could be valuable natural sources of natural antimicrobial molecules. Plant extracts containing volatile (e.g., essential oils) and non-volatile antimicrobial molecules can be distinguished. Plant essential oils are outside the scope of this review. This review will thus provide an overview of current knowledge regarding the promises and the limits of phenolic-rich plant extracts for food preservation and biofilm control on food-contacting surfaces. After a presentation of the major groups of antimicrobial plant phenolics, of their antimicrobial activity spectrum, and of the diversity of their mechanisms of action, their most promising sources will be reviewed. Since antimicrobial activity reduction often observed when comparing in vitro and in situ activities of plant phenolics has often been reported as a limit for their application, the effects of the composition and the microstructure of the matrices in which unwanted microorganisms are present (e.g., food and/or microbial biofilms) on their activity will be discussed. Then, the different strategies of delivery of antimicrobial phenolics to promote their activity in such matrices, such as their encapsulation or their association with edible coatings or food packaging materials are presented. The possibilities offered by encapsulation or association with polymers of packaging materials or coatings to increase the stability and ease of use of plant phenolics before their application, as well as to get systems for their controlled release are presented and discussed. Finally, the necessity to consider phenolic-rich antimicrobial plant extracts in combination with other factors consistently with hurdle technology principles will be discussed. For instance, several authors recently suggested that natural phenolic-rich extracts could not only extend the shelf-life of foods by controlling bacterial contamination, but could also coexist with probiotic lactic acid bacteria in food systems to provide enhanced health benefits to human.

The challenge of exploiting polyphenols from olive leaves: addition to foods to improve their shelf-life and nutritional value

Olive leaves represent a waste from the olive oil industry which can be reused as source of polyphenols. The most representative phenolic compound of olive leaves is the secoiridoid oleuropein, followed by verbascoside, apigenin-7-O-glucoside, luteolin-7-O-glucoside, and simple phenols. The attention towards these compounds derives above all from the large number of studies demonstrating their beneficial effect on health, in fact olive leaves have been widely used in folk medicine in the Mediterranean regions. Moreover, the growing demand from consumers to replace the synthetic antioxidants, led researchers to conduct studies on the addition of plant bioactives in foods to improve their shelf-life and/or to obtain functional products. The current study overviews the findings on the addition of polyphenol-rich olive leaf extract (OLE) to foods. In particular, the effect of OLE addition on the antioxidant, microbiological and nutritional properties of different foods is examined. Most studies have highlighted the antioxidant effect of OLE in different food matrices, such as oils, meat, baked goods, vegetables, and dairy products. Furthermore, the antimicrobial activity of OLE has been observed in meat and vegetable foods, highlighting the potential of OLE as a replacer of synthetic preservatives. Finally, several authors studied the effect of OLE addition with the aim of improving the nutritional properties of vegetable products, tea, milk, meat and biscuits. Advantages and drawbacks of the different use of OLE were reported and discussed. © 2020 Society of Chemical Industry.

Environmental Impact of Food Preparations Enriched with Phenolic Extracts from Olive Oil Mill Waste

Reducing food waste as well as converting waste products into second-life products are global challenges to promote the circular economy business model. In this context, the aim of this study is to quantify the environmental impact of lab-scale food preparations enriched with phenolic extracts from olive oil mill waste, i.e., wastewater and olive leaves. Technological (oxidation induction time) and nutritional (total phenols content) parameters were considered to assess the environmental performance based on benefits deriving by adding the extracts in vegan mayonnaise, salad dressing, biscuits, and gluten-free breadsticks. Phenolic extraction, encapsulation, and addiction to the four food preparations were analyzed, and the input and output processes were identified in order to apply the life cycle assessment to quantify the potential environmental impact of the system analyzed. Extraction and encapsulation processes characterized by low production yields, energy-intensive and complex operations, and the partial use of chemical reagents have a non-negligible environmental impact contribution on the food preparation, ranging from 0.71% to 73.51%. Considering technological and nutritional aspects, the extraction/encapsulation process contributions tend to cancel out. Impacts could be reduced approaching to a scale-up process.

Gluten-Free Breadsticks Fortified with Phenolic-Rich Extracts from Olive Leaves and Olive Mill Wastewater

Nowadays, food processing by-products, which have long raised serious environmental concerns, are recognized to be a cheap source of valuable compounds. In the present study, incorporation of phenolic-rich extracts (500 and 1000 mg kg⁻¹) from olive leaves (OL) and olive mill wastewater (OMW) into conventional gluten-free formulations has been exploited as a potential strategy for developing nutritious and healthy breadsticks with extended shelf-life. To this end, moisture, water activity (a_w), visual and textural properties, the composition of biologically active compounds (soluble, insoluble, and bio-accessible polyphenols), antioxidant activity, oxidation stability, and consumer preference of the resulting breadsticks were investigated. Fortified breadsticks had higher moisture and a_w, lower hardness, and similar color in comparison to the control, especially in the case of OL extract supplementation. All enriched formulations significantly affected the phenolic composition, as evidenced by the decrease in insoluble/soluble polyphenols ratio (from 7 in the control up to 3.1 and 4.5 in OL and OMW, respectively), and a concomitant increase in polyphenol bio-accessibility (OL: 14.5–23% and OMW: 10.4–15% rise) and antioxidant activity (OL: 20–36% and OMW: 11–16% rise). Moreover, a significant shelf-life extension was observed in all fortified breadsticks (especially in case of OMW supplementation). Sensory evaluation evidenced that 61% of the assessors showed a marked, but not significant, tendency to consider the sample supplemented with high levels of OL as a more palatable choice.

Functional compounds from olive pomace to obtain high-added value foods - a review

Olive pomace, the solid by-product from virgin olive oil extraction, constitutes a remarkable source of functional compounds and has been exploited by several authors to formulate high value-added foods and, consequently, to foster the sustainability of the olive-oil chain. In this framework, the aim of the present review was to summarize the results on the application of functional compounds from olive pomace in food products. Phenolic-rich extracts from olive pomace were added to vegetable oils, fish burgers, fermented milk, and in the edible coating of fruit, to take advantage of their antioxidant and antimicrobial effects. Olive pomace was also used directly in the formulation of pasta and baked goods, by exploiting polyunsaturated fatty acids, phenolic compounds, and dietary fiber to obtain high value-added healthy foods and / or to extend their shelf-life. With the same scope, olive pomace was also added to animal feeds, providing healthy, improved animal products. Different authors used olive pomace to produce biodegradable materials and / or active packaging able to increase the content of bioactive compounds and the oxidative stability of foods. Overall, the results highlighted, in most cases, the effectiveness of the addition of olive pomace-derived functional compounds in improving nutritional value, quality, and / or the shelf-life of foods. However, the direct addition of olive pomace was found to be more challenging, especially due to alterations in the sensory and textural features of food. © 2020 Society of Chemical Industry.

Determination of the Variability of Biophenols and Mineral Nutrients in Olive Leaves with Respect to Cultivar, Collection Period and Geographical Location for Their Targeted and Well-Timed Exploitation

The interactive effects of cultivar, collecting period, and geographical location on the content and composition of biophenols and macro and micronutrients in olive (Olea europaea L.) leaf were investigated. Leaves of six cultivars were collected at three periods in two locations in Croatia. The leaves of Istarska bjelica cultivar had the greatest biophenol (oleuropein) potential, especially those sampled in January and in March at the location of Pag. All the cultivars yielded leaves with the highest concentration of biophenols in March, which coincided with the pruning period. Except for high oleuropein concentration in Istarska bjelica, flavonoids were found to be most useful for differentiating olive leaves according to cultivar. Verbascoside turned out to be the most potent differentiator of collecting periods, while phosphorus and zinc turned out to be most useful for differentiating locations. Despite different agroecological conditions at the two locations, cultivar exhibited a significant effect on olive leaf nutrient composition, which was certainly causally related to that of the biophenols. The results obtained showed that it is possible to plan more well-timed and efficient exploitation of biophenols from olive leaf based on the knowledge about the interactive effects of the three studied factors.

Evolution of VOC and Sensory Characteristics of Stracciatella Cheese as Affected by Different Preservatives

Undesired volatile organic compounds (VOCs) can negatively affect the flavor of fresh food products; especially those characterized by a mild and delicate aroma. Finding connections between chemical and sensory analyses is a useful way to better understand the arising of off-flavors. A study was conducted on stracciatella; a traditional Italian cream cheese that is emerging on international markets. Samples were prepared by adding two different preservatives (alone or combined): sorbic acid and an olive leaf extract. Their influence on flavor preservation during refrigerated storage was investigated by chemical, microbiological and sensory analyses. A strong change of the VOC profile was ascertained after 8 days in the control cheese and in the sample added with leaf extract alone. The samples containing sorbic acid, alone or in combination with leaf extract, gave the best chemical and sensory results, demonstrating a significant shelf-life extension. In particular, these samples had lower concentrations of undesired metabolites, such as organic acids and volatiles responsible for off-flavor, and received better scores for odor and taste. Ex and Ex-So samples had significantly higher antioxidant activity than Ctr and So throughout the entire storage period, and the color parameter shows no differences among samples taken on the same day. The use of the olive leaf extract, at the concentration tested, seemed to be interesting only in the presence of sorbic acid due to possible synergic effect that mainly acted against Enterobacteriaceae.

Vegetable Additives in Food Packaging Polymeric Materials

Plants are the most abundant bioresources, providing valuable materials that can be used as additives in polymeric materials, such as lignocellulosic fibers, nano-cellulose, or lignin, as well as plant extracts containing bioactive phenolic and flavonoid compounds used in the healthcare, pharmaceutical, cosmetic, and nutraceutical industries. The incorporation of additives into polymeric materials improves their properties to make them suitable for multiple applications. Efforts are made to incorporate into the raw polymers various natural biobased and biodegradable additives with a low environmental fingerprint, such as by-products, biomass, plant extracts, etc. In this review we will illustrate in the first part recent examples of lignocellulosic materials, lignin, and nano-cellulose as reinforcements or fillers in various polymer matrices and in the second part various applications of plant extracts as active ingredients in food packaging materials based on polysaccharide matrices (chitosan/starch/alginate).