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 Milk Quality Focus Causation or Correlation?
  Untangling the mysteries of non-foaming milk
Erin Cuthbert, Provincial Dairy Technologist, BC Ministry of Agriculture
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low, but a high proportion of susceptible milk due to coinciding factors can lead to high bulk tank FFA.
Nutrition also plays a role in the production of susceptible milk. Low energy intake in early and late lactation, high carbohydrate diets, and diets with high percentages of concentrates can induce susceptible milk production. High butyric acid content in wet forages can increase the risk of milk rancidity, which is linked to non-foaming milk. Work with a herd nutritionist to ensure that your herd’s nutrition program isn’t compromising milk quality.
Milk Temperature and Cooling
A variation of spontaneous lipolysis is temperature-induced lipolysis, and occurs when precooled milk is warmed above 25C, and then re-cooled to below 10C. In practice, this can occur when fresh milk is added to a bulk tank containing cooled milk from previous milkings. The second parlour milking has been shown to be the biggest concern because equal parts of warm milk are added to cooled milk in the tank. For robotic systems, small volumes of milk already present in the tank will undergo temperature fluctuations with each new addition of milk. Minimizing temperature fluctuations is an important factor in reducing the risk of lipolysis. In both instances, “susceptible” milk is more likely to be affected than “normal” milk.
The impact that lipolysis can have on milk quality is a complex issue because of the multiple factors involved, but there are steps that can be taken to identify and eliminate contributors to non-foaming milk. If your FFA is trending upwards, the first step is to try to identify the type of lipolysis, so you know where to look – induced versus spontaneous, or in some cases both. Lipolysis can continue once the milk has left the farm and a serious non-foaming issue can impact the entire bulk tanker and silo at the processing plant. Once pasteurized, the lipase enzyme is inactivated and the FFA level with stabilize. Butensuringthathighqualitymilkreaches the processing plant has and always will be the responsibility of the dairy producer.
The Ministry and Milk Board are continuing to actively investigate the issue, collecting extensive data to better understand the complexity so that clearer guidelines can be determined.
“Non-foaming milk” might be the most (un) popular term circulating the dairy industry these past few months. Although it may seem like a superficial issue, it is important to remember that non-foaming milk is not only the cause of a poorly made latté, it is an issue that can impact cheese and other milk products, produce off-flavours, and impact shelf-life. Unlike other milk quality challenges such as a high somatic cell count or high bacteria count, non-foaming milk is an issue that not only impacts the individual producer, it impacts the entire milk route.
Before we dive into the issue of non- foaming, it is important to have a basic understanding of the cause of non-foaming – Lipolysis.
Lipolysis is the enzymic hydrolysis (breakdown) of the milk fat globule into free fatty acids (FFAs) and partial glycerides, altering the biochemistry of the milk and depressing its foaming ability. There are two main types of enzymes that are responsible for the detrimental effects of lipolysis – those that are present in milk and those that are of microbial origin. This article will focus specifically on the lipase enzyme present in milk.
Lipoprotein lipase is the major milk- enzyme and accounts for the majority of lipolytic activity. A minimal amount of lipolysis occurs naturally in milk, unless the milk fat globule membrane becomes compromised allowing lipase to cleave the fat(triglyceride)intopartialglyceridesand free fatty acids (FFAs).
Multiple factors can influence the degree of lipolysis, tipping the scales towards a non-foaming outcome. Proper handling and storage conditions will not greatly increase the FFA content of milk after it is harvested from the cow. When lipolysis activity leads to elevated FFAs, it can be categorized as “induced” or “spontaneous” lipolysis, and the amount of stress a milk fat globule can withstand reflects its integrity which is sometimesgivena“normal”or“susceptible” milk classification.
“Induced” lipolysis is the result of the milk fat globule becoming physically or chemically damaged, allowing the lipase enzyme to access the fat substrate. “Spontaneous” lipolysis is triggered when milk is cooled below 10C after milking and will occur regardless of the physical stress placed on the milk. “Normal” milk will not undergo significant lipolysis unless it is significantly damaged by the milking
system. In contrast, “susceptible” milk will undergo spontaneous lipolysis regardless of the physical stress it is placed under.
Induced Lipolysis
The source of this stress placed on the milk after it is harvested can include, but is not limited to, the milking system’s air intake, milk pumping activity, milk pipeline size and length, agitation, and milk cooling parameters. The extent to which induced lipolysis occurs will depend on the severity and duration of the stressor, the amount of lipase present, and the integrity of the milk fat globule membrane. The more severe the treatment, or the longer the exposure, the greater the disruption to the milk fat globule membrane and the resulting surface area of the exposed fat globule
• Air Intake and Agitation
Excessive air intake can increase FFA levels by rupturing the milk fat globule membrane. Discrepancies in air intake alone are unlikely to cause significant changes in FFA; however, when coupled with vigorous agitation (i.e. high air intake at the milking cluster, milk pumping, over agitation in the bulk tank) or low milk yield, the incorporation of air damages the milk fat globule. Over-agitation of the milk further weakens the milk fat globule membrane, increasing its susceptibility of the triglycerides to the lipase enzyme.
• Milk Cooling and Mixing
Efficient milk cooling that avoids over- agitation and temperature fluctuations of milk is essential to maintaining the integrity of the milk fat globule membrane. Precooling milk before the bulk tank can reduce the risk of non-foaming; however, freezing and thawing of milk can disrupt the milk fat globule membrane. Research suggests that milk volumes in bulk tanks should cover a minimum of half up to the entire agitator paddle, before agitation and cooling are initiated to reduce the risk of over mixing.
Induced lipolysis can be caused by multiple areas along the milking and cooling system however, regular maintenance of milking equipment can reduce the likelihood of compounding lipolytic causes leading to an elevated FFA. Under normal circumstances, milk can withstand various amounts of stress placed on it from the cow to the bulk tank. In one study, mechanical treatment of the fat globules during milking only accounted for 20% of FFA variation among experiments, compared to 59% to 75% that were explained by
differences between cows such as milk yield, fat percentage, and fat globule size. In a nutshell, not all milk is created equal. In some instances, we must look beyond the technical causes of non-foaming and explore milk production at ground zero – the milking herd.
Spontaneous Lipolysis
The factors that largely determine the susceptibility of milk to spontaneous lipolysis are the amount of lipase activity in the milk, the size and integrity of the milk fat globule, and the balance of lipolysis-activating and inhibiting factors. Susceptible milk can be produced by most, if not all cows, but because of individual cow characteristics and their milk’s response to various factors, only a proportion of cows in a herd should produce susceptible milk at any one time under normal circumstances. The production of susceptible milk by an individual cow is due to different variables such as stage of lactation, nutrition, and milk production, all of which can’t be considered independent variables because they are interdependent on one another. Cows in late lactation have the greatest tendency to produce susceptible milk due to the milk fat membrane being in a less protective state and being more likely to produce milk containing activator lipoproteins. This may be due in part to stage of gestation and lower energy intakes, as well as decreasing milk volumes per milking. Overmilking cows in anystageoflactationcanincreaseFFAdue to globule weakness and a low milk volume per litre of air ratio, which was a significant factor for robotic milking systems in one study. Milk from late lactation cows, and susceptible milk in general, are at a higher risk of agitation-induced lipolysis.
Once susceptible milk is cooled in the bulk tank, spontaneous lipolysis is activated and occurs rapidly at first, before naturally leveling off over time. However, even small volumes of susceptible milk can impact an entire tank of milk due to the lipase- activating factor in the milk that can create a chain reaction within the tank environment.Thisisespeciallyconcerning if induced lipolysis is weakening the milk fat globule of “normal” milk produced by most of the herd. “Normal” milk does have an inhibitory effect against the lipase activity of “susceptible” milk, though, and can prevent extensive lipolysis if the ratio of normal milk in the bulk tank is high compared to susceptible milk. Normally, the extent of lipolysis in a milk bulk tank is
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