Lipase-catalyzed Lipolysis Of Milk Fats: Influence On Flavour Improvement And Triacylglycerol Redistribution

Dairy milk fat remains valuable components of human diet due to their balanced nutritive value and pleasant flavour.There has been a new trend at both the food manufacturer and consumer to keep away from the use of artificial flavour to the natural flavour,due to recent studies on health concerns/claims which forces the regulatory authorities trying to limit the use of artificial flavour in the processed foods and beverages.With the increasing interest in natural products by consumers for instance milk fat flavour,more emphasis has been directed to the production of natural flavour.Bovine milk fat is a kind of animal fat that is third among the most a widely consumed fat type.Due to its pleasant flavour,milk fat is now widely processed to produce/improve different kinds of flavour that are stable and safe and can be added to different food products such as bakery products,coffee creamers and other food products as ingredients.The whole research work is focused on the importance of lipases on milk fat treatments to produce desired flavour and furthermore,to investigate their storage stability.The interest in application of biocatalysis during natural milk fat flavour development has increased rapidly and lipases have become the most studied group in the development of bovine milk fat flavour.Lipozyme-435,Novozyme-435 and Thermomyces lanuginosus Immobilized(TLIM)were used to hydrolyze anhydrous milk fat(AMF)and anhydrous buffalo milk fat(ABF)and their volatile flavour compounds were identified by solid-phase micro-extraction gas chromatography/mass spectrometry(SPME-GC/MS)and then compared at three different hydrolysis intervals.Both AMF and ABF after lipolysis produced high amount of butanoic and hexanoic acids and other flavour compounds;however,highest amount were produced by Lipozyme-435 and Novozyme-435 followed by TL-IM.The hydrolyzed products were assessed for oxidative stability and found both that,for AMF and ABF treated lipase samples,Lipozyme-435 and TL-IM were generally more stable compared to Novozyme-435.For both AMF and ABF treated lipase,Lipozyme-435 was observed to cause no further oxidation consequences which indicates Lipozyme-435 was stable during hydrolysis at 55 oC for 24 hours.In order to develop/improve the milk fat flavour,the use of relevant processing method that can shorten the processing time is highly appreciated.Ultrasonic microwave assistance extraction(UMAE)was used to establish its relevance for the production of volatile compounds by using milk fats treated with lipases.AMF and ABF were used in the development of milk fat flavour by using three different lipases.AMF and ABF were hydrolyzed by Lipozyme-435,Novozyme-435 and Thermomyces lanuginosus using UMAE set at 50 oC under low ultrasonic microwave irradiation in 45 minutes.SPME-GC/MS was used to identify the volatile compounds.Butanoic and hexanoic acids were produced in high amount by both AMF and ABF after lipolysis compared with other volatile compounds.The highest amount of butanoic acids was produced by Novozyme-435(>86%),Lipozyme-435(>81%),whilst Thermomyces lanuginosus(>57%).Thermomyces lanuginosus,Lipozyme-435 and Novozyme-435 also produced high amount of hexanoic acids more than 21,10 and 9% peak areas respectively.In addition,the oxidative stability of both lipolyzed products and the control were assessed and found that,both AMF and ABF after lipolysis were generally more stable compared to the control.Fourier transform infrared was used to analyze both treated and un-treated lipases and had shown that UMAE influenced the lipase activity by changing Amide I and II bands.The study also investigated the triacylglycerol(TAGs)remained after hydrolysis under mechanical shaking.The TAGs from AMF were hydrolyzed by Lipozyme-435 and Novozyme-435 and later on analyzed by using ultra-performance liquid chromatography system coupled with quadrupole time-of-flight mass spectrometry(Qu-ToF-MS).The results revealed that the percentages of TAGs(CN 28–34)and TAGs(CN 36–42)with at least two short chain fatty acids and with short and medium chain fatty acids were respectively decreased after 24 hours of hydrolysis.On the other hand,TAGs(CN 44–54)with at least two long chain fatty acids were found to increase in both Lipozyme-435 and Novozyme-435 treated AMF.Meanwhile,the melting and crystallization profiles of both Lipozyme-435 and Novozyme-435 treated AMF were modified and significantly different when compared with the untreated AMF.Furthermore,the study was also used low irradiation of ultrasonic microwave assisted extraction on lipases mixed with AMF or ABF,with the aim of hydrolyzing TAGs,especially those containing short chain fatty acids.Lipozyme-435,Novozyme-435 and Thermomyces lanuginosus were mixed with phosphate buffer and either AMF or ABF in a jacketed flask.The reaction mixtures were exposed to low irradiation UMAE under temperature control(50 °C ± 2 °C)for 45 minutes.An ultra-performance liquid chromatography system coupled with Qu-ToF-MS was used to analyze TAGs in AMF and ABF after lipolysis.The re-distribution was evidenced by the presence of a higher percentage of TAGs with at least two medium-chain fatty acids and one long-chain fatty acid,and a high percentage of TAGs with long-chain fatty acids as a consequence of a decreased percentage of TAGs with short-chain fatty acids.Furthermore,the melting and crystallization profiles were modified in both AMF and ABF treated with lipases in comparison to just AMF or ABF.Finally,the study investigated the volatile compounds of AMF and ABF treated lipases that was stored during a period of one-year storage.It was found that general both AMF and ABF treated lipases were stable during the storage periods when compared with either AMF or ABF samples.The study was also monitored by measuring the level of oxidative stability of the samples during 12 months of storage.The results revealed that AMF and ABF treated lipases were general stable at the end of the storage study and their oxidative stability were almost the same value as either of AMF or ABF before 12 months of storage.