Impacts of Oil Types and Storage Conditions on Milk Fat Quality of Strained Yogurt Immersed in Oil

Abstract

To maintain strained yogurt freshness, it was shaped into balls (3-3.5 cm diameter), completely immersed in oil, and stored at refrigerated or ambient temperature for 6 months. The impacts of immersing strained yogurt in oil on the topped oil and product's final quality of lipids including fat oxidation, lipolysis, cholesterol oxidation, and conjugated linoleic fatty-acid content (CLNA) (i.e., as freshness indicators), during storage under various storage conditions, were evaluated. Peroxide value (PV), 7-keto-cholesterol, free fatty acids (FFA), and CLNA content were also determined. When stored in light, FFA of strained yogurt immersed in olive or corn oil increased from 0.44 to 1.29 and from 0.12 to 0.58, respectively. Olive oil-topped and corn oil-topped samples exposed to light had 48.9 and 7.9 (meq O 2 kg −1 ) PV, respectively. Similar trends were reported for strained yogurt fat during storage for up to 6 months. Storage conditions showed little to no effects on the rate of fat and cholesterol oxidation, fat lipolysis, and CLNA content. Strained yogurt freshness indicators were maintained during the extended storage duration without refrigeration. The freshness indicators have a significant impact on enhancing consumer preference of strained yogurt.

Compositional Changes in the Extra Virgin Olive Oil Used as a Medium for Cheese Preservation

“…The content of FFA (expressed as % of oleic acid), used to monitor the hydrolytic degradation of lipids, increased in EVOOs stored with the addition of cheese, especially after two months ( Table 1 ). The expansion of FFA was also reported by Al-Ismail et al [ 4 ] for olive oil samples stored with strained yogurt balls for two months in dark at room temperature (23.3 °C). Generally, the esters of long-chain FFAs (present in EVOO) do not hydrolyze easily [ 33 ].…”

“…The obtained results ( Table 1 ) have shown that the presence of any type of cheese caused no major increases in the PV of topping oils, considering that the levels remained slightly above those of control oils. The same occurrence was noted in EVOOs used as topping oil for strained yogurt balls in which PV was unchanged, even lower, compared to fresh EVOO during two-month storage in the dark and at 4 °C [ 4 ].…”

“…This natural type of food preservation is traditionally employed in the Mediterranean countries mainly due to the reduced food exposure to oxygen, oxidative stability of predominant monounsaturated oleic fatty acid, and richness in EVOO natural antioxidants. Despite long-term application on various food products and the probability of mutual migration and interaction of ingredients, there is little research on this topic, particularly as regards dairy products preserved by immersion in olive oil [ 4 , 5 , 6 ].…”

“…To the best of our knowledge, such interactions have not been taken into consideration in real storage conditions considering food in long-term contact with EVOO. A small number of studies investigated this matter under real-time storage conditions of different foods, such as vegetables [ 18 , 19 ] or strained yogurt [ 4 , 5 ]. Although, none of them considered the phenolic content of the used oil.…”