The Potential of Olive Leaf Extract as a Functional Ingredient in Yoghurt Production: The Effects on Fermentation, Rheology, Sensory, and Antioxidant Properties of Cow Milk Yoghurt

Abstract

Background: Yoghurt has been traditionally consumed for its high nutritional value and health-promoting benefits. The addition of plant extracts as a source of phenolic compounds and bio-flavonoids has attracted much attention recently since milk and dairy products are deficient in these health-protecting components. Accordingly, olive leaf extract (OLE) has been considered due to the presence of bioactive compounds, primarily polyphenols. Thus, the aim of this research was to investigate the possibility of adding OLE into cow milk yoghurt as a potential functional ingredient. Methods: Yoghurts enriched with OLE (1.5, 3, and 5% v/v) were produced and compared with yoghurt without OLE. In all samples acidity, viscosity, colour, syneresis, water holding capacity (WHC), microbiological parameters, sensory properties, total phenols, and antioxidant activity (DPPH and FRAP methods) were determined. Results: The addition of OLE resulted in shorter fermentation and lower pH, but it had no adverse effect on the viability of yoghurt starter bacteria. OLE-enriched yoghurts showed increased syneresis, higher total phenols content, and antioxidant activity, while WHC and viscosity decreased. Sensory properties were slightly poorer for yoghurts containing higher OLE concentrations. Considering all of the obtained results, the addition of 1.5% OLE appeared to be optimal.

Production of Acid and Rennet-Coagulated Cheese Enriched by Olive (Olea europaea L.) Leaf Extract—Determining the Optimal Point of Supplementation and Its Effects on Curd Characteristics

“…In general, it was found that the addition of OLE significantly (p < 0.0001) increased the TP in all cheese samples as well as in the remaining whey, regardless of the coagulation method (p > 0.05). The obtained results are consistent with previously published data [8,[42][43][44][45]. The increase in TP corresponds to the increase in the effective concentration of the added OLE, except in the sample EM 25, where the TP was the highest, probably due to the variations in the dewatering process.…”

“…An increase in AA was also observed in the whey remaining after acid coagulation, which was significantly higher compared to enzymatic coagulation (p < 0.0001), correlating with the results of the TP (Figure 3). Although the influence of OLE on the AA of cheese has not been studied in detail, some previous studies have also shown that the addition of OLE leads to an increase in the antioxidant activity of yogurt [8,19] and kefir [54]-dairy products that are also produced by acid coagulation.…”

“…Accordingly, several authors have explored the possibilities of adding OLE to dairy products [11,[17][18][19]. In line with this, our previous study [8] focused on the supplementation of cow's milk yoghurt with OLE. We found that the addition of OLE resulted in shorter fermentation and had no negative effects on the viability of yoghurt starter bacteria.…”

“…Dairy products such as cheese and fermented milk are considered as some of the most popular functional food matrices due to their significant share in the dairy products market, frequent consumption, and acceptance by healthconscious consumers [6,7]. Moreover, cheese and fermented milk represent a suitable medium for fortification with nutritionally valuable compounds, especially plant extracts containing phenolic compounds that are absent in milk and dairy products [7][8][9]. Since Mediterranean agriculture relies heavily on the cultivation of olives and the production of olive oil [10], large quantities of olive leaves remain after processing [11].…”

Evaluation and improvement of antioxidant activity and physicochemical properties of yogurt enriched with Persian gum (Amygdalus scoparia Spach) and fennel (Foeniculum Vulgare) extrac

“…Similarly, Ghasempour et al (2012) that of Amirdivani and Baba (2013), who reported that adding 2% green tea extract to yogurt reduced its apparent viscosity. Barukčić et al (2022) reported that the presence of olive leaf extract led to a reduction in yogurt viscosity, which was more or less proportional to the olive leaf extract concentration. These reports reveal the effect of plant extracts related to plant type and their concentration (Haji Ghafarloo et al, 2019).…”