If you have been reading about Water activity and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Last reviewed on 2026-04-24. Where a claim depends on a specific study, the study is described rather than over-claimed.
Industrial production begins with whey protein concentrate or isolate dispersed in water. Selected proteases, such as trypsin, pepsin, or microbial enzymes, are added under controlled pH and temperature. Hydrolysis continues until a target hydrolysis level is reached, after which heat or pH adjustment inactivates the enzyme. Ultrafiltration, diafiltration, and ion exchange may remove larger peptides, salts, or residual lactose. The liquid is then concentrated and spray-dried into powder. Processing choices influence peptide size, bitterness, mineral content, and microbial quality.
Analytical control focuses on protein content, hydrolysis extent, molecular weight distribution, and residual intact protein. Kjeldahl or Dumas methods measure total nitrogen, while size-exclusion chromatography or mass spectrometry estimates peptide profiles. Sodium dodecyl sulfate polyacrylamide gel electrophoresis can show remaining intact proteins, though small peptides may not resolve. Enzyme-linked immunosorbent assays are used to assess residual allergenic proteins in some contexts. Because no single method captures all relevant features, manufacturers combine several assays and report values against internal specifications.
Stability depends on moisture, temperature, oxygen, and packaging. Powdered hydrolysate generally requires cool, dry storage and protection from humidity because peptides can absorb water and undergo Maillard reactions with residual lactose. Higher temperatures can increase bitterness, discoloration, and loss of solubility over time, while liquid hydrolysate formats are more perishable and may need refrigeration or preservatives. Shelf-life studies typically monitor moisture, color, pH, protein solubility, and microbial counts. Exact stability limits vary by peptide profile, packaging, and water activity, so general rules should be treated as approximate.
Whey protein hydrolysate is a dairy ingredient made by treating whey protein with enzymes or, less often, acid or heat to break peptide bonds. The starting material is typically sweet whey or acid whey from cheese making, first concentrated and dried into whey protein concentrate or isolate. Hydrolysis shortens long protein chains into smaller peptides, changing functional properties such as solubility, viscosity, and foam formation. The resulting powder contains peptides, residual intact protein, moisture, minerals, and variable amounts of lactose and fat depending on the starting material.
Enzymatic hydrolysis usually uses proteases from microbial, plant, or animal sources. The enzyme choice, pH, temperature, and reaction time determine which peptide bonds are cleaved and the final peptide profile. After hydrolysis, the enzyme is inactivated by heat, and the mixture is clarified, filtered, concentrated, and spray-dried. Manufacturers may use ultrafiltration to remove larger peptides or minerals. The degree of hydrolysis, often reported as a percentage, describes the proportion of peptide bonds broken. A higher degree generally means shorter peptides, but it does not by itself define taste, allergenicity, or biological activity.
Whey protein hydrolysate appears in foods, infant formula, sports nutrition, and specialized clinical nutrition. Its production can reduce viscosity and improve heat stability compared with intact whey protein. Bitterness is common because short hydrophobic peptides can activate bitter taste receptors. The ingredient is not the same as free amino acids; it remains a mixture of peptides of different lengths. Composition varies by supplier, enzyme, and process, so two hydrolysates with the same protein content may behave differently in a formulation.
| Property | Value | Notes |
|---|---|---|
| Moisture content | ≤ 6% for powder | Lower moisture supports shelf stability |
| Water activity | Often below 0.3 | Higher values increase caking and browning |
| Typical storage temperature | 15–25 °C | Cool, dry, protected from humidity |
| Common analytical method | Size-exclusion chromatography | Estimates peptide molecular weight distribution |
| Bulk density | 0.3–0.6 g/mL | Depends on spray-drying and particle size |
Peptide size distribution is central to product characterization because biological and functional effects often depend on molecular weight. Size-exclusion chromatography, reversed-phase high-performance liquid chromatography, and capillary electrophoresis can separate peptides by size or hydrophobicity. Mass spectrometry provides sequence-level information and can detect marker peptides, though it is less common for routine lot release. For allergen control, enzyme-linked immunosorbent assays estimate residual intact protein or specific milk proteins, but results depend on antibody recognition and may not detect small peptides. No single method captures the full composition.
Stability and storage practices affect measured quality over time. Hydrolysate powders are hygroscopic and can absorb moisture, leading to caking, Maillard browning, and reduced solubility. Cool, dry storage in sealed containers limits these changes, while high humidity and warm temperatures accelerate them. Microbiological testing for total aerobic counts, yeasts, molds, and specified pathogens is typical for food ingredients. Regulatory status varies by country; in many jurisdictions hydrolyzed whey protein is regulated as a food ingredient rather than a drug, and claims about reduced allergenicity require specific substantiation.
Composition reflects the whey source and the extent of hydrolysis. Beta-lactoglobulin and alpha-lactalbumin fragments are common, and sweet whey may contribute glycomacropeptide. The amino acid profile remains broadly similar to intact whey protein, but peptide size affects how quickly nitrogen appears in blood after ingestion. Bitter notes often arise from short peptides with hydrophobic residues. Hydrolysates are used in sports nutrition, infant formula, and clinical nutrition, though effects on muscle, immunity, or allergy risk are separate research questions rather than guaranteed properties.
Whey protein hydrolysate is derived from whey, the liquid byproduct of cheese-making or casein coagulation. It consists of peptides and free amino acids produced when peptide bonds are cleaved by enzymes or acid. Hydrolysis lowers the average molecular weight and can change solubility, viscosity, and bitterness. The degree of hydrolysis indicates the proportion of peptide bonds broken and distinguishes partial from extensive hydrolysates. Commercial ingredients vary widely in peptide size, mineral content, and lactose level.
Production usually starts with whey protein concentrate or isolate. The material is dissolved, pasteurized, and adjusted to conditions that favor a chosen protease, such as trypsin, pepsin, or papain. Enzyme choice, pH, temperature, and reaction time determine peptide length, terminal residues, and functional behavior. After hydrolysis, the enzyme is inactivated by heat or pH change, and the liquid is clarified, filtered, concentrated, and dried. Membrane filtration can further fractionate peptides and remove some minerals or lactose. The final powder is typically spray-dried.
=== Collection === Blood cultures are typically drawn through venipuncture. Collecting the sample from an intravenous line is not recommended, as this is associated with higher contamination rates, although cultures may be collected from both venipuncture and an intravenous line to diagnose catheter-associated infections. Prior to the blood draw, the top of each collection bottle is disinfected using an alcohol swab to prevent contamination. The skin around the puncture site is then cleaned and left to dry; some protocols recommend disinfection with an alcohol-based antiseptic followed by either chlorhexidine or an iodine-based preparation, while others consider using only an alcohol-containing antiseptic to be sufficient. If blood must be drawn for other tests at the same time as a blood culture, the culture bottles are drawn first to minimize the risk of contamination. Because antimicrobial therapy can cause false negative results by inhibiting the growth of microbes, it is recommended that blood cultures are drawn before antimicrobial drugs are given, although this may be impractical in people who are critically ill. A typical blood culture collection involves drawing blood into two bottles, which together form one "culture" or "set". One bottle is designed to enhance the growth of aerobic organisms, and the other is designed to grow anaerobic organisms. In children, infection with anaerobic bacteria is uncommon, so a single aerobic bottle may be collected to minimize the amount of blood required.
=== Single-particle measurements === Generally speaking single-particle measurement instruments desorb particles one at a time using a pulsed laser. The process is called laser desorption/ionization (LDI) and is the primary ionization method used for single-particle measurements. The main advantage of using LDI over thermal desorption, is the ability to analyze both non-refractory and refractory (e.g., mineral dust, soot) components of atmospheric aerosols. Laser vaporization allows precise laser firing when individual particles fly through the vaporization zone, and the systems are thus dubbed single particle mass spectrometers (SPMS). Several versions of SPMS have been reported, including the aerosol time-of-flight mass spectrometer (AToFMS), the laser mass analyzer for particles in the airborne state (LAMPAS), particle analysis by laser mass spectrometer (PALMS), the rapid single-particle mass spectrometer (RSMS), the bioaerosol mass spectrometer (BAMS) b194 Steele et al., 2003), the nanoaerosol mass spectrometer (NAMS), the single-particle laser ablation time-of-flight mass spectrometer (SPLAT), the single-particle aerosol mass spectrometer (SPAMS), and laser ablation aerosol particle time-of-flight mass spectrometer (LAAP-ToF-MS). Among the most commons of these instruments is the aerosol time-of-flight mass spectrometer (AToFMS).
== Research == Guselkumab has undergone phase III clinical trials comparing it with adalimumab (Humira) and ustekinumab (Stelara). The safety and efficacy of guselkumab was compared to a placebo and to adalimumab in the "VOYAGE 1" and "VOYAGE 2" phase III clinical trials (ClinicalTrials.gov IDs: NCT02207231 and NCT02207244). Preliminary results indicated that a significantly higher proportion of patients taking guselkumab had better skin clearance compared to those taking the other treatments. At week 16, 73.3% of patients taking guselkumab achieved a PASI 90 (90% reduction in PASI score from baseline), vs 49.7% of those taking adalimumab; additionally, 91.2% of patients taking guselkumab achieved a PASI 75 (75% reduction in PASI score from baseline), vs 73.1% of those taking adalimumab. The phase III clinical trial "NAVIGATE" (ClinicalTrials.gov ID: NCT02203032) included only patients who had poor responses to treatment with ustekinumab. It showed that patients who switched to guselkumab from ustekinumab did better than those who remained on ustekinumab.
Sources: en.wikipedia.org
=== Other liquids === For example, hydrogen fluoride—which has three lone pairs on the F atom but only one H atom—can form only two bonds. Ammonia has the opposite problem: three hydrogen atoms but only one lone pair.
==== Homozygous ==== By definition, the forms of MODY are autosomal dominant, requiring only one abnormal gene to produce the disease; the severity of the disease is moderated by the presence of a second, normal allele which presumably functions normally. However, conditions involving people carrying two abnormal alleles have been identified. Unsurprisingly, combined (homozygous) defects of these genes are much rarer and much more severe in their effects.
=== In apricot === Apricot as a climacteric fruit undergoes fast post-harvest maturation. The latent PPO form can spontaneously activate during the first weeks of storage, generating the active enzyme with a molecular weight of 38 kDa. Ascorbic acid/protease combinations constitute a promising practical anti-browning method as treated apricot purees preserved their color.
=== Cognitive development === Protein-calorie malnutrition can cause cognitive impairments. This most commonly occurs in people who were malnourished during a "critical period ... from the final third of gestation to the first 2 years of life". For example, in children under two years of age, iron deficiency anemia is likely to affect brain function acutely, and probably also chronically. Similarly, folate deficiency has been linked to neural tube defects. Iodine deficiency is "the most common preventable cause of mental impairment worldwide." "Even moderate [iodine] deficiency, especially in pregnant women and infants, lowers intelligence by 10 to 15 I.Q. points, shaving incalculable potential off a nation's development." Among those affected, very few people experience the most visible and severe effects: disabling goiters, cretinism and dwarfism. These effects occur most commonly in mountain villages. However, 16 percent of the world's people have at least mild goiter (a swollen thyroid gland in the neck)."
Sources: en.wikipedia.org
=== Hypothyroidism === The rate of hypothyroidism is around six times higher in people who take lithium. Low thyroid hormone levels in turn increase the likelihood of developing depression. People taking lithium thus should routinely be assessed for hypothyroidism and treated with synthetic thyroxine if necessary. Lithium associated thyroid dysfunction is reversible and thyroid levels return to normal if lithium is discontinued. However, hypothyroidism can be corrected by treatment with thyroxine and does not require the lithium dose to be adjusted.
=== Mass average molar mass === The mass average molar mass (often loosely termed weight average molar mass) is another way of describing the molar mass of a polymer. Some properties are dependent on molecular size, so a larger molecule will have a larger contribution than a smaller molecule. The mass average molar mass is calculated by
== History == In the Standard Model (SM), matter stability is described by assigning a baryon number B=+1 to the proton (lightest baryon), following Hermann Weyl's 1929 proposed conservation principle. Ernst Stueckelberg formally postulated the baryon number (heavy charge at the time) conservation law in 1939. In the 1950s it was realized that limits on proton decay were exceedingly long. The very existence of advanced life forms on Earth implied
The Mesopotamians seem to have had little interest in the natural world as such, preferring to study how the gods had ordered the universe. Animal physiology was studied for divination, including especially the anatomy of the liver, seen as an important organ in haruspicy. Animal behavior too was studied for divinatory purposes. Most information about the training and domestication of animals was probably transmitted orally, but one text dealing with the training of horses has survived. The ancient Mesopotamians had no distinction between "rational science" and magic. When a person became ill, doctors prescribed both magical formulas to be recited and medicinal treatments. The earliest medical prescriptions appear in Sumerian during the Third Dynasty of Ur (c. 2112 – c. 2004 BCE). The most extensive Babylonian medical text, however, is the Diagnostic Handbook written by the ummânū, or chief scholar, Esagil-kin-apli of Borsippa, during the reign of the Babylonian king Adad-apla-iddina (1069 – 1046 BCE). In East Semitic cultures, the main medicinal authority was an exorcist-healer known as an āšipu. The profession was passed down from father to son and was held in high regard. Of less frequent recourse was the asu, a healer who treated physical symptoms using remedies composed of herbs, animal products, and minerals, as well as potions, enemas, and ointments or poultices. These physicians, who could be either male or female, also dressed wounds, set limbs, and performed simple surgeries.
Secret police and armed forces were ordered to initiate large-scale incursions into the houses of protest planners and independent journalists "once each sector has been cleansed of wanted people", Ba'athist paramilitaries were to occupy these areas under protection of Syrian military and prevent survivors from returning to their homes Formation of "joint investigation committees" headed by leaders of the Baathist security departments across all provinces to incarcerate suspected activists and cross-examining them in prisons Transfer of the findings across all security branches for pinpointing of additional suspects The commands were passed down to the provincial leaders of the party who were instructed to swiftly execute the orders in their respective regions
Sources: en.wikipedia.org
Hydrolysis extent is often estimated by measuring the increase in soluble nitrogen or free amino groups relative to total nitrogen. The o-phthaldialdehyde method and trinitrobenzenesulfonic acid assay are common laboratory approaches. Values are method-dependent, so comparisons require the same assay and calculation.
Enzymatic cleavage can expose hydrophobic amino acid residues that interact with bitter taste receptors. The intensity depends on peptide sequence, hydrolysis extent, and further processing such as filtration or deamidation. Bitterness is not a reliable indicator of protein quality or allergenicity.
Moisture uptake, storage temperature, and packaging barrier properties are major factors. Residual lactose can participate in browning reactions when water activity and temperature rise. Shelf-life testing usually combines accelerated and real-time conditions to estimate change in color, solubility, and microbial stability.
It is whey protein that has been partially broken down into smaller peptides through hydrolysis. The powder still contains a mixture of peptides, residual protein, minerals, and other whey components. It is used as a food ingredient rather than a single pure compound.