Acoustic Particle Sizing of Milk

超聲法粒度分析在乳劑行業(yè)的應用

Oil/Water, as well as, Water/Oil emulsions can partially degrade or even fully break up upon undergoing dilution. Thus, particle size measurements without dilution are desirable for emulsion characterization.

油/水以及水/油的乳液會在稀釋之后部分降解甚至*分解。因此，在不稀釋的情況下直接測量乳液的粒徑是一種理想方法。

The APS-100 Acoustic Particle Sizer1 measures -without the need for sample dilution Particle Size Distribution, Longitudinal Viscosity, Percent Solids, pH, Conductivity, and Temperature. Using a patented measurement design2, the APS-100 performs acoustic attenuation spectroscopy measurements in the ultrasonic range of 1-100 MHz.

美國MAS公司生產的APS-100超聲法粒度儀《1》可以不用稀釋，直接測量粒度分布，縱向粘度，固含量，PH值，電導率及溫度。通過測量設計《2》，APS-100可以在1-100MHz的超聲波范圍內進行聲學衰減光譜測量。

The resulting attenuation spectrum of dB/cm vs. Frequency (MHz) is used by a patented first-principle algorithm3 to calculate particle size distribution data without making assumptions regarding the shape of the particle size distribution, e.g. unimodal, bimodal, lognormal, Gaussian, etc. The APS-100 is calibrated with water without the need for particle size calibration standards.

通過使用原理算法使用產生的dB/cm / 頻率（MHz）的衰減譜來計算粒徑分布數(shù)據(jù)，而無需對粒徑分布的形狀進行假設，例如單峰、雙峰、對數(shù)正態(tài)、高斯等。APS-100是用水進行校準的，不需要使用粒度校準標準。

APS measurements are made by low-power (inaudible) short acoustic pulses (about 10 microseconds long) that do not affect the sample’s dispersion state as depicted in figure 1. Another instrument, the Zeta-APS, measures Zeta potential in addition to all these parameters.

APS測量采用低功率(聽不清)短聲脈沖(約10微秒長)，不影響圖1所示的樣品的分散狀態(tài)。另外Zeta-APS儀器，除了測量上述所有這些參數(shù)外，還測量Zeta電位。

Fig. 1. Waveforms of the ultrasonic pulses applied and measured during Acoustic Particle Sizing.

圖1 - 超聲波脈測量粒度的過程中，超聲波的脈沖波形。

Fig. 2. Acoustic Attenuation Spectra of 4% wt silica-water sample (3 runs: ♦, ■, ▲) alongside DI water (x).

圖2 - 4%wt二氧化硅水樣（3次：♦, ■, ▲)和去離子水的聲衰減譜。

Fig. 3. Particle Size Distribution overlaid data for three consecutive runs of a 4% wt silica-water sample.

圖3 – 三次4%wt二氧化硅水樣的粒度分布數(shù)據(jù)疊加圖

Figures 2 and 3 show attenuation spectra and particle size distribution data for three consecutive runs of a silica-water sample at 4% wt percent solids level (Nissan Chemical, Houston, TX). A water (solvent) spectrum is also shown. A solvent spectrum (excluding the particles) is required for particle size computation.

圖2和圖3顯示了連續(xù)三次4%wt二氧化硅水樣的粒度分布和聲衰減譜（Nissan Chemical, Houston, TX）。水樣的譜圖也有顯示。粒徑計算需要溶劑譜(不包括微粒)。圖3所示的PSD在0.1微米有相當窄的分布，接近MP1040二氧化硅的標稱平均粒徑。

Emulsion Analysis

乳液測試分析

For this study, five consumer-type dairy samples were characterized as follows:

在本研究中，五種消費型乳液樣本的特征如下：

- Half and Half Cream (HHC) 半脂乳

- Whole Milk (WM) 全脂乳

- 1% Low-fat Chocolate Milk (CM) 1% 低脂巧克力乳 

- 1% Low-fat Milk (LFM) 1% 低脂乳

– Nonfat Milk (NFM) 脫脂乳

The samples were analyzed without dilution. They were continuously mixed by the APS- 100’s onboard mechanical mixer. Sample temperature was kept at 26 ºC by the APS- 100’s sample heater.

這些樣品沒有進行稀釋。他們是由APS-100的內置機械混合器連續(xù)混合。通過APS-100的加熱系統(tǒng)，保證樣品在26℃。

Acoustic Data

超聲數(shù)據(jù)

Fig. 4. Acoustic Attenuation Spectra for five milk samples.

圖4 – 5種乳劑樣品的超聲衰減波譜。

Figure 4 shows acoustic attenuation spectra, dB/cm vs. Frequency (MHz), for the five milk samples. Attenuation levels decrease in the following order due to each sample’s fat content level as follows (see below about the 1% chocolate milk sample):

HHC > WM > CM > LFM > NFM

圖4顯示了5種乳的dB/cm / 頻率（MHz）的衰減譜。由于每個樣品的脂肪含量水平，衰減水平按以下順序降低（見下文關于1%巧克力牛奶樣品）：

HHC半脂乳 > WM全脂乳 > CM1% 低脂巧克力乳 > LFM 低脂乳> NFM脫脂乳

Regarding Chocolate vs. Low-fat milk, the difference in attenuation is due to the added chocolate flavor components.

關于巧克力和低脂乳，衰減的差異是由于添加了巧克力風味成分。

These samples were analyzed at 26 ºC, kept constant by the APS-100’s onboard heater. Also, the samples were continuously mixed during these measurements by the APS-100’s mechanical mixer.

這些樣品在分析過程中通過APS的加熱系統(tǒng)保持溫度在26℃。此外，在這些測量過程中，由APS-100的機械混合器連續(xù)混合樣品。

Fig. 5. Particle size distribution data for a whole milk sample by Acoustic Particle Sizing (APS-100).

圖5 – APS-100測量的全脂乳的粒度分布數(shù)據(jù)。

Figure 5 below presents the particle size distribution for a whole milk sample analyzed without dilution. The fat-free milk sample was used to represent the intrinsic attenuation required by the acoustic particle sizing computations4.

圖5顯示了未經(jīng)稀釋而分析的全脂乳的粒度分布。脫脂乳樣品用于表示聲學顆粒尺寸計算所需的固有衰減《4》。

Intrinsic attenuation corresponds to the solvent attenuation, i.e. attenuation excluding the discrete phase (particles/droplets) of the sample. The particle and solvent physical properties required by the particle size computations were obtained from published data5.

固有衰減對應于溶劑衰減，即不包括樣品的離散相（顆粒/液滴）的衰減。顆粒尺寸計算所需的顆粒和溶劑物理性質是從已發(fā)表的數(shù)據(jù)中獲得的《5》。

Some of the corresponding particle size data for the whole milk sample are as follows:

全脂乳樣品的相應粒度數(shù)據(jù)如下

Mean particle size, Volume weighted: 1.8 µm, 25th, 75th percentiles: 0.9, 2.5 µm

Mean particle size, Area weighted: 1.1 µm, 25th, 75th percentiles: 1.46, 1.5 µm

體積平均粒徑：1.8μm，D25 為0.9μm，D75為2.5μm

面積平均粒徑：1.1μm，D25 為1.46μm，D75為1.5μm

Figure 6 above corresponds to a sample of half and half creamer measured by an APS- 100 instrument without dilution. The particle size data is as follows:

Mean particle size, Volume weighted: 1.45 µm, 25th, 75th percentiles: 0.53, 2.6 µm

Mean particle size, Area weighted: 0.65 µm, 25th, 75th percentiles: 0.2, 0.68 µm

圖6對應的是用APS- 100儀器測量的沒有稀釋半脂乳樣品的測試數(shù)據(jù)：

體積平均粒徑：1.45μm，D25 為0.53μm，D75為2.6μm

面積平均粒徑：0.65μm，D25 為0.20μm，D75為0.68μm

REFERENCES

1. Matec Applied Sciences, Northborough, MA USA, www.matecappliedsciences。。ｃｏｍ)

2. US Patent 6,604,408

3. US Patent 6,119,510

4. McClements, D. J., and Povey, J. W., Ultrasonic analysis of edible fats and oils, Ultrasonics, vol 30, 6, 1992.

5. Lopez, C., Briard-Bion, V., Camier, B., Gassi, J. Y., Milk Fat Thermal Properties and Solid Fat Content in Emmental Cheese: A Differential Scanning Calorimetry Study, J. Dairy Sci., 89:2894-2910, 2006/