Ultrasonication has been widely studied in bovine milk but the effects of ultrasound (US) on the buffalo's milk fat globules (MFG) are not well known yet. In this study, buffalo's milk samples were ultrasonicated at 20 kHz and physicochemical properties were assessed under different processing conditions. Shear homogenization was performed with 1188 J/mL energy density for the comparison. Results show that ultrasonication reduced the average volume-weighted mean diameter (D[4,3]) of MFG by 93% and increased the surface area by a factor of 8.5 compared to the native counterparts. The zeta-potential (ZP) of MFG are increased by ultrasonication compared to fresh milk (−26.37 vs. −18.22 mV) indicating better stability. Changing the pH of ultrasonicated milk to the isoelectric pH (pI) reduced the zeta-potential (ZP) by −19.8 mV and increased the (D[4,3]) > 0.4 mm indicating the gelation. The size of milk particles increased up to 76–586 μm and the ZP was reduced by 3.1 mV with the increase of ionic strength from 50 to 200 mM. Heating of milk at 90 °C for 30 min increased D[4,3] in US homogenized milk by 22%. Both ultrasonication and shear-homogenization increased the free saturated fatty acids by 2.75–3 g/100 g fat compared to raw buffalo's milk. Ultrasonication increased the gel hardness by 98% compared and shear-homogenized milks. The results of this study indicate that the ultrasonication reduced the size of buffalo's MFG up to sub-micron level with superior stability while improving (P < 0.05) the gels strength compared to shear-homogenization.

Industrial relevance

Buffalo set-yoghurts made with unhomogenized milk exhibit higher syneresis and poor stability upon shear-induced breakdown, which are mainly due to the porous gel structure containing a large number of bigger fat globules. Under the large scale production, buffalo set-yoghurts are often fortified with dairy/non-dairy solids and stabilizers in order to prevent this problem. However, the use of some inexpensive, non-food grade alternatives are also reported in some parts of the world for the cottage or medium level production of buffalo yoghurts. In this work, it was shown that ultrasonication with the energy density of 1188 J/mL can be used to produce buffalo set-yoghurts with superior gel strength and therefore, can be used as an unconventional approach to improve the product quality.

中文翻译：

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超声波对牛奶脂肪球的物理化学性质水牛（水牛）加工条件下进行：用剪切均化的比较

超声波已经在牛乳中进行了广泛的研究，但是超声波（US）对水牛乳脂球（MFG）的影响尚不为人所知。在这项研究中，水牛的牛奶样品在20 kHz下进行了超声波处理，并在不同的加工条件下评估了其理化特性。为了进行比较，以1188 J / mL的能量密度进行了剪切均质化。结果表明，与天然超声相比，超声处理使MFG的平均体积加权平均直径（D [4,3]）降低了93％，表面积增加了8.5倍。与新鲜牛奶相比，通过超声处理，MFG的Zeta电位（ZP）有所提高（-26.37 vs.-18.22 mV），表明稳定性更好。将超声牛奶的pH更改为等电pH（pI）将ζ电位（ZP ）降低了-19.8 mV，并使（D [4,3]）> 0.4 mm增大，表明发生了凝胶化。随着离子强度从50 mM增加到200 mM，牛奶颗粒的大小增加到76–586μm，ZP减少3.1 mV。将牛奶在90°C下加热30分钟，可使美国均质牛奶中的D [4,3]增加22％。与生水牛的牛奶相比，超声和剪切均质化均使游离饱和脂肪酸增加2.75–3 g / 100 g脂肪。超声和剪切均质的牛奶相比，凝胶硬度提高了98％。这项研究的结果表明，与剪切均质化相比，超声处理可将水牛的MFG尺寸减小至亚微米水平，具有出色的稳定性，同时可提高（P <0.05）凝胶强度。

行业相关性

用未均质的牛奶制成的水牛城定型酸奶表现出较高的脱水收缩性，并且在剪切诱导的分解作用下稳定性较差，这主要归因于多孔凝胶结构包含大量较大的脂肪小球。在大规模生产下，水牛定型酸奶通常用乳制品/非乳制品固体和稳定剂来强化，以防止出现此问题。但是，在世界某些地区，也有报道称，一些廉价，非食品级的替代品被用于水牛酸奶的平房或中档生产。在这项工作中，表明能量密度为1188 J / mL的超声可用于生产具有优异凝胶强度的水牛定型酸奶，因此可作为提高产品质量的非常规方法。