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For example: does consumption of vinegar somehow change digestion of flour (bread, cakes, pasta, puffs) ? May be there are some benefits to eat flour meal with vinegar ?
In the case you're talking about (just using vinegar to taste), there should be no effect whatsoever on a healthy stomach. The stomach already contains a significant amount of acid, and a little bit more from the acetic acid in vinegar won't change much, just like eating some citrus fruit with a meal (oranges, lemons, and whatnot) won't change much. Acid-mediated hydrolysis of chewed food is only the first of many steps in digestion - a significant portion is performed by enzymes and commensal microorganisms in the gut. Changing the type or amount of acid by a small amount won't affect anything significantly in the long run.
The only exception I can think of is for people suffering from peptic ulcers, whether from over-use of NSAIDs (Non-Steroidal Anti-Inflammatory Drugs such as aspirin, ibuprofen, naproxen, etc.), infection with H. pylori, or possible genetic/developmental issues (most often seen in young children). In these cases, consuming an overly-acidic meal may aggravate the symptoms of peptic ulceration.
Salad Dressing Science: Emulsion Lab
If you’ve ever tried to make salad dressing from scratch, you know that one of the biggest challenges is getting the oil and the vinegar to mix properly. No matter how hard you try to shake, stir, or whisk oil and vinegar together, they eventually separate. This happens because vinegar and oil are made of very different types of molecules that are attracted to their own kind.
The electronegative oxygen in a water molecule pulls electrons away from the two hydrogens, creating an uneven distribution of charge within the molecule.
Most vinegars are solutions of acetic acid and water (plus some other acids and alcohols, depending on the type of vinegar you are using). Water, acetic acid, and alcohol are all examples of polar molecules—molecules that have a slightly negative charge at one end, or pole, and a slightly positive charge at another end. These slightly charged poles arise because one or more atoms in the molecule are electronegative, meaning that they tug electrons—which are negatively charged—towards them, creating an uneven distribution of charge within the molecule. Polar molecules are generally attracted to other polar molecules because their slightly negative poles have an affinity for their slightly positive poles. Polar molecules are attracted to water molecules—which are also polar—and are called hydrophilic, which means “water loving.”
Oils are a different story. Oils are a type of fat (like butter, shortening, and lard) and are considered non-polar. Fats and oils are composed primarily of long molecules called fatty acids (usually bound together by glycerol molecules into groups of three called triglycerides). Most of the atoms in a fatty acid molecule share electrons evenly and are neither negatively nor positively charged (although fatty acids do contain small regions of polarity—just not enough to make the whole molecule polar.) Non-polar molecules love other non-polar molecules and will glom together when mixed with water. You can observe this phenomenon by placing a few drops of oil on the surface of a bowl of water—eventually the drops will form a single large oil slick. Oils repel polar molecules such as those found in vinegar. Because oils also repel water, they are called hydrophobic, which means “water-fearing.”
The carbon (black) and hydrogen (white) in this non-polar fatty acid molecule share electrons evenly and are neither negatively or positively charged.
How can we bring together polar and non-polar molecules to make something delicious like mayonnaise (which is essentially a combination of water and oil) or salad dressing? We need an emulsifier. Emulsifiers are the hand-holders of the molecule world. They contain both hydrophobic and hydrophilic regions and are able to attract and “hold hands” with polar and non-polar molecules simultaneously, pulling them together to form a special type of mixture called an emulsion. For instance, after adding an effective emulsifier to oil and vinegar and mixing thoroughly, separation of the oil from the vinegar will take much longer or won’t happen at all.
The Research on Vinegar
The most popular vinegar used in supplemental form or externally for skin conditions is apple cider vinegar (ACV). Cider vinegar contains between 5 percent and 6 percent acetic acid. The research connecting vinegar to lowered blood glucose levels has been done since 1988, published in the June issue of the Journal of Agricultural and Biological Chemistry. Since then, vinegar has been the focus of numerous studies regarding its effect on diabetes, weight gain and loss, and appetite control.
Apple cider vinegar uses are primarily as a weight loss aid and for blood sugar control. However, Harvard Medical School has stated that the evidence for this is slim. There is some evidence for apple cider vinegar benefits for people with diabetes. Taking a dose before meals may help to lessen spikes in blood sugar by blocking the absorption of starch. University of Chicago Medicine affirms that taking 20 grams of apple cider vinegar before meals is a harmless, and possibly helpful, way to prevent blood glucose spikes.
Claims regarding apple cider benefits consist of its ability to reduce blood pressure, to cure cancer and to treat heartburn. These myths are unsubstantiated, and there is very little to no evidence that vinegar will work in any of these cases.
Vinegar comes from French "vin aigre", aka sour wine. The transformation of wine into vinegar happens when some (possibly unwanted) aerobic bacteria transform the alcohol into acetic acid by oxidation. So any alcoholic mixture which allows growth of those bacteria can be turned into vinegar, like cider, sake.
The amount of acetic acid depends on the alcohol content which in turn depends on the initial concentration of sugar. It is also dependent on the time allowed for fermentation.
In fact it is much more complicated than that. Have a look at Wikipedia for more info.
My 3.785 L, extra strength 6% "Acitity" vinegar (V), means (1), and I just found this out myself. Vinegar produced by the Generator Method, which produces anhydrous acetic acid. The pure Acetic acid (Ac) crystalizes to a solid at less then 16.7 C. (2). You can imagine how easy it is to make any concentration you want, when you have a powder to mix with water = distilled vinegar. That means that in that 3.8 L bottle only about 270g is actually Acetic Acid. However because Acetic Acid is a weak acid in water with a pH of
2.2 (= ) for 6% acidity. Some of that Acetic Acid (moles of Ac - mole of protons = moles of acetic acid left) dissociates so, there is some (equal to
Production of Vinegar
Production methods and varieties of vinegars
Vinegar is produced from raw materials containing starch or sugar via sequential ethanol and acetic acid fermentations (FAO/WHO 1982 ) and is used in a variety of food applications (Türker 1963 Tan 2005 ). Grape, apple, and other fruit juices are the primary starting materials used for vinegar production (Adams 1985 ) although rice vinegar, malt vinegar, and beer vinegar are also produced in some countries. The production of vinegar typically involves a first fermentation where simple sugars in raw material are converted to alcohol by yeasts. The resultant alcohol is further oxidized to acetic acid by AAB during the last fermentation (Gullo and Giudici 2008 ). Several methods of vinegar production exist but primarily 2 methods are used commercially. The first is a traditional method classified as a “surface method” in which the culture of AAB grows on the surface of wood shavings and provides oxygen at the surface. The second method, classified as a “submerged culture” is a method in which oxygen is supplied in fermentation to accelerate industrial production (Garcia-Parilla and others 1997 ). The general production method for vinegar is shown in Figure 1.
A wide variety of different vinegars are produced around the world. Some of the vinegar varieties are listed in Table 1 and classified according to origin of production. One of the most famous vinegar varieties is the traditional balsamic vinegar produced from cooked and concentrated musts of white or red grapes (Masino and others 2008 ). The resultant vinegar product is aged in a successive set of progressively smaller barrels ranging in volume from 75 to 10 L (Giudici and others 2009 ).
|Vinegar varieties||Major production countries|
|Apple cider vinegar||World wide|
|Champagne vinegar||France, United States|
|Coconut vinegar||Southeast Asian|
|Distilled vinegar||United States|
|Red wine vinegar||World wide|
|Rice vinegar||United States, Taiwan|
|Tarragon vinegar||United States|
|White wine vinegar||Turkey, Italy|
Sherry vinegar is made from Sherry wines following traditional methods of acetification in the Jerez–Xérès–Sherry, Manzanilla de Sanlúcar and Vinagre de Jerez Denomination of Origin regions of southwest Spain (Mejias and others 2002 ). The unique aroma and flavor of Sherry vinegar is due to the traditional method of production followed in this region known as the “soleras y criaderas” system. This system involves a slow acetification during aging in American oak casks stacked in rows and levels. The final product is blended from the stacked casks across a mixture of vinegars of differing ages (Parrilla and others 1999 Alonso and others 2004 ).
Other vinegars produced around the world include the Japanese vinegar Kurosu and the Chinese vinegar Zhenjiang which are produced from rice (Nishidai and others 2000 Xu and others 2007 ). Production of rice vinegar begins with immersion of rice in water, heating, cooling, and inoculation with yeast to produce ethanol. Subsequently, an acetic acid fermentation is conducted and the product is matured (Chen and Chen 2009 ). Cane vinegar is made from fermented sugarcane juice, has a mild flavor and is used extensively in food preparation in the Philippines (Tan 2005 ). Persimmons are considered a medicinal fruit in traditional Chinese medicine and persimmon vinegar is produced in China (Ubeda and others 2011 ). In China, the plant known as Radix Ophiopogon japonicus (mondo grass, dwarf lily turf, liriope) is used as a traditional medicinal herb ophiopogon vinegar produced from Radix O. japonicus is a popular functional food in China (Lin and others 2011 ). Malt vinegar has a hearty flavor and is produced from fermented barley and grain mash in England (Horiuchi and others 1999 ). Yacon (Smallanthus sonchifolius) is a South American tuberous plant that is an abundant source of prebiotic fructooligosaccharides which are fermented into vinegar (Ojansivua and others 2011 ).
PH and acidity – their difference and importance in vinegar
Those who know vinegar know acidity is of prime importance in measuring the completion and strength of vinegar. Acetic acid is what distinguishes vinegar and global standards of taste and safety specify minimum acidity levels for vinegar. The more widely recognized measurement of the strength of an acid (or base) is the pH scale. Many people know pH is important for controlling microbes and a maximum level of 4 (under 3.7 is better) is required for any application where rogue microbes could cause issues in food or sauce preservation. Please note you should consult local and FDA regulations as well as acidified food guidelines before settling on a pH and water activity for any preserved food.
The most easily measured value is pH. Everything from $10 meters to professional meters like my own that are hundreds of dollars can be used to give an instant pH reading. Acidity measurements are more technical and careful. The typical method is titration using a strong base like sodium hydroxide (NaOH) to determine the percent acid in vinegar. Percent acid is defined as the number of grams of acetic acid per 100 mL of vinegar. So the 5% vinegar you buy in the store has 5 g of acetic acid per 100 mL (or 50g per L). Vinegar makers occasionally use the term ‘grain’ which is just the acidity multiplied by 10 so 5% acidity is 50 grain.
Many people default to pH to see how done their vinegar is given the difficulty of measuring acidity which requires specialized chemicals and lab equipment like a burrette and ring stand. There are also basic chemistry calculations required that, while not difficult, can be daunting for some. For measuring the basic progress of vinegar and its microbial safety, pH is acceptable. However, for using homemade vinegar for canning and for selling vinegar commercially, pH can be deceptive and even dangerous.
First, canning requires a minimum recommended acidity (typically 5%) because the dilution of the vinegar in recipes still requires a minimum level of acid. Remember pH is a logarithmic scale. An acid pH of 3 is 10 times more acidic than that of a pH of 4.Vinegar only measured by pH risks being too low in acidity and can be diluted too much which is dangerous for canning where preventing botulism and other bugs is paramount. As will be explained later, pH cannot replace acidity because the pH can vary widely for different types of vinegar of the same acidity.
To understand their difference, let’s look at how they are calculated. Warning – chemistry ahead.
First pH. An acid is a chemical compound that contains a positive charged hydrogen ion (H + ) combined with a negative charged so-called “conjugate base”. In water, both parts dissociate and the H + concentration is what defines pH. The H + ion, combines loosely with water to make an ion called Hydronium H30 + whose concentration is often used in lieu of H + in equations and pH calculations.
The formula for acetic acid is CH3COOH and CH3COO – is the conjugate base.
For acetic acid, dissociation in H2O yields
Now all of the reactants (left side) and products (right side) have equilibrium concentrations in the solution. The concentration of a chemical, in terms of moles/liter, is designated with square brackets. So the concentration of acetic acid is [CH3COOH]. At standard temperature (25 C) and pressure (1 atm) the equilibrium constants for acid dissociation (acid dissociation constant) Ka determines the relative concentrations in equations like the below:
Ka is usually calculated to neglect the water in the reactants. The pH is the negative logarithm (base 10) of the H30 + concentration, pH=-log10 [H30 + ]. You often see Ka shown as pKa where pKa =-log10Ka. For acetic acid, Ka and pKa are 1.76 x 10 -5 and 4.75 respectively at standard temperature and pressure.
So for example, let’s take 5% acetic acid like the standard grade sold in retail stores. 50 g per liter of acetic acid where the molar mass of acetic acid is 60 g means these vinegars are 0.83M (M stands for molar or moles/liter). Given Ka and the fact that 1 mole of CH3COO – is generated per mole of H30 + in the reaction we can see that the concentration [H30 + ] is 3.8 x 10 -3 M and pH should be 2.4.
On the other hand, when you mesaure acidity you are titrating vinegar with a base until you find out what volume of base makes all the acetic acid disappear. The H30 + concentration or acid dissociation constant has little relevance except in how fast the titration occurs.
So why aren’t they interchangeable in some nifty formula? Here is the deal: take two different acids with the same acidity in g/100 mL. So 5% vinegar and 5% hydrochloric acid (HCl). First, their pH levels are different because 1) the molar mass of each acid is different so their molar concentrations vary at the same acidity and 2) their acid dissociation constants vary so different amounts of [H30 + ] come out in equilibrium.
But there are still complications even if we have the same acid, as in different types of vinegar. I know you are saying, “OK acidity and pH aren’t the same and pH varies for different acids but a pH of 2.4 is equivalent to a 5% acidity acetic acid, right?”
Well, not quite. Even though white distilled vinegar approaches this pH level at 5%, no vinegar gets that low. The main reason is most natural vinegars have many other compounds in the vinegar, including organic acids and other exotic compounds. Some even have small amounts of bases (for example many fruits) and these help increase the ‘buffering capacity’ of the vinegar. A buffer is a mixture of an acid and its conjugate base in proportions that resist pH changes with added acid or base. Finally, there is a reaction called esterification where the acetic acid reacts with leftover ethyl alcohol in the vinegar to form flavor chemicals called esters. The main one is ethyl acetate and this is present in all vinegars. The small levels of other organic acids like formic acid and tartaric acid (in grapes) also form their own esters. These reactions consume acetic acid. This isn’t a bad thing since the amount is usually not large and the development of esters in the aging process helps make vinegar less sharp.
So what you end up seeing are pH levels that are wildly different for vinegars of the same acidity. White distilled vinegar of 5% can range from a pH of 2.5 to 2.7 on average. Pineapple vinegar ranges from 2.8 to 2.9. Red and white wine vinegar can be low, 2.6 to 2.8 but this is helped by the other acids like tartaric acid from grapes. The highest is apple cider vinegar which is typically 3.3 to 3.5 at 5%. It is also one of the chemically more complex vinegars.
So the bottom line is pH and (titratable) acidity both have importance but are not interchangeable or even predictable across vinegars. If you are making the same vinegar from roughly the same raw material over and over, there may be a relation that can be worked out but it will be hard to generalize. So if you are doing canning with home vinegar, make sure you measure the acidity yourself or send it to a local wine lab or university food lab for measurement. Definitely if you want to sell your vinegar you have a legal requirement to make sure the acidity exceeds 4%.
The Chemistry of Coppers
- Put a couple of centimetres of each liquid into a separate glass.
- Put a copper coin into each glass. If you can balance them half in the liquid and half out that will make any changes really easy to see.
- After a couple of minutes, take the coins out and dry them on the kitchen towel. Don't forget which coin went in which liquid!
- Compare the coins. Which liquid made the colour of the coins change the most?
Some liquids such as vinegar, lemon juice, orange juice Cola etc. all cause the coins to become cleaner, if you leave the coins half in the liquid they will become stripey. The half in the liquid will be clean and a pink colour, but the half that was out of the liquid will have stayed the same.
|Copper with an oxide layer on the right.|
All the liquids which had an effect on the coins are what's called acids. Acids tend to be very sour tasting things. When coins are left in your pocket for a long time, the copper in them reacts with the oxygen in the air and turns into copper oxide. That's the black gunky stuff on the outside of the coin. When you put that in an acid it will dissolve the copper oxide leaving behind just the shiny metal coin. Basically, if you ever want to clean any metals, acid is a good thing to do it with!
The acid has some hydrogen in it which will react with the oxygen in the oxide and turn into water. The more hydrogen atoms in the acid, the stronger the acid, the lower its pH, and the more shiny the coins will appear after being soaked. Vinegar is the strongest acid in our sample.
Once some of the hydrogens have dissolved the oxide and turned into water, this leaves the other half of the acid, which in vinegar is called the acetic group. So some of the copper is dissolved in that and sits around in solution. If you take lots and lots of coins and leave them in very strong vinegar for about an hour and you can see a slight green tinge. That's the copper in the copper acetate which looks slightly green. You definitely don't want to drink that!
This does also mean that cola drinks are corrosive and can dissolve your teeth in just the same way it dissolves the copper oxide. Cola drinks contain vast quantities of phosphoric acid. In fact, a certain global cola company is one of the world's largest consumers of phosphoric acid. It means that cola has a pH of about 3 or 3.5, just slightly different from dilute hydrochloric acid that you may use in labs at school.
Why do the coins go pink?
The coins go pink which is actually the colour of clean copper, what we call 'copper coloured' is the pink copper covered with a thin layer of black copper oxide.
What Is the Chemical Composition of Vinegar?
Vinegar is a liquid that is produced from the fermentation of ethanol into acetic acid. The fermentation is carried out by bacteria.
Vinegar consists of acetic acid (CH3COOH), water and trace amounts of other chemicals, which may include flavorings. The concentration of the acetic acid is variable. Distilled vinegar contains 5-8% acetic acid. Spirit of vinegar is a stronger form of vinegar that contains 5-20% acetic acid.
Flavorings may include sweeteners, such as sugar or fruit juices. Infusions of herbs, spices and other flavors may be added, too.
Vinegar is made from a variety of source materials. Each contributes its own unique flavor signature to the final product. Vinegar may be made from sugar cane juice, rice and other grains, grapes (balsamic vinegar), coconut water, fruit wines, kombucha, or apple cider. Spirit vinegar is a strong variety of vinegar (5% to 21% acetic acid) made from sugar cane and doubly fermented. The first fermentation changes sugar into alcohol, while the second fermentation changes alcohol into acetic acid.
Cabbage Chemistry--Finding Acids and Bases
You might have done experiments with well-labeled acids and bases in school, but have you ever wondered whether a certain food or chemical around the house is an acid or a base? You can find out using a red cabbage to make an indicator solution.
When two or more ingredients are entirely dissolved in one another, you have a solution. For example, mixing salt with water creates a clear solution, even though the salt is there and the solution tastes salty. When mixed with water, whether a chemical "donates" a charged particle (called an ion) to the solution&mdashin this case, a hydrogen ion&mdashor "accepts" one from it determines whether it's an acidic or basic solution. An indicator changes color when exposed to such a mixture, depending on whether the solution is acidic or basic.
Acids are solutions that lose hydrogen ions and usually taste sour. Some very common household solutions are acids, such as citrus fruit juices and household vinegar. Bases are solutions that pull hydrogen ions out of solution and onto themselves, "accepting" them, and usually feel slippery. Bases have many practical uses. For example, "antacids" like TUMS are used to reduce the acidity in your stomach. Other bases make useful household cleaning products.
To tell if something is an acid or a base, you can use a chemical called an indicator. An indicator changes color when it encounters an acid or base. There are many different types of indicators, some that are liquids and others that are concentrated on little strips of "litmus" paper. Indicators can be extracted from many different sources, including the pigment of many plants. For example, red cabbages contain an indicator pigment molecule called flavin, which is a type of molecule called an anthocyanin. Very acidic solutions will turn an anthocyanin red whereas neutral solutions will make it purplish and basic solutions will turn it greenish-yellow. Consequently, the color an anthocyanin solution turns can be used to determine a solution's pH&mdasha measure of how basic or acidic a solution is.
&bull A small red cabbage
&bull Pot of boiling water
&bull Two large bowls or pots
&bull Tablespoon measurer
&bull Large spoon (optional)
&bull Three or more small, white paper cups (small, white paper drinking glasses or dishes will also work)
&bull Goggles or other protective eyewear
&bull Lemon or lime juice
&bull Bleach-based cleaning product
&bull Other foods to test, such as clear soda pop, baking soda solution, egg whites, tomatoes, cottage cheese (optional)
&bull Grate a small red cabbage. If you do not want to grate the entire cabbage, grating half of a cabbage should be enough. Put the fine, pulpy grated cabbage into a large bowl or pot.
&bull Boil a pot of water. Use caution when handling the boiling water. Pour the boiling water into the bowl with the cabbage pulp until the water just covers the cabbage.
&bull Leave the cabbage mixture steeping, stirring occasionally, until the liquid is room temperature. This should take at least half an hour. The liquid will become red or purplish-red in color.
&bull Place a strainer over another large bowl or pot and pour the cabbage mixture through the strainer to remove the cabbage pulp. Press down on the pulp in the strainer, such as by using a large spoon, to squeeze more liquid out of the pulp.
&bull In the bowl, you should now have only liquid that will either be purple or blue in color. This will be your indicator solution, which you will use to test the pH of different liquids.
&bull Children should wear goggles or other protective eyewear and adults should supervise and use caution when handling bleach and vinegar, because they can irritate eyes and skin.
&bull Fill a small, white paper cup, drinking glass or white dish with one tablespoon of your cabbage-indicator solution. What is the color of your indicator solution?
&bull Add drops of lemon or lime juice to the indicator solution until you see the solution change in color. Gently swirl the solution and make sure the color stays the same. What color did the solution become?
&bull The color of the solution will change depending on its pH: Red color indicates the pH is 2 Purple indicates pH 4 Violet indicates pH 6 Blue indicates pH 8 Blue-green indicates pH 10 Greenish-yellow indicates pH 12.
&bull Based on its color, what is the pH of the lemon or lime juice solution?
&bull In another small, white paper cup, add one tablespoon of your original cabbage-indicator solution. Add drops of vinegar until you see the solution change color. What color did the vinegar solution become? What is the pH of the solution?
&bull In a third small, white paper cup, add one tablespoon of your original cabbage-indicator solution. Handling it with caution, add drops of the bleach cleaning product until you see the solution change color. What color did the bleach solution become, and what does this indicate about its pH?
&bull If you want to test the pH of other foods, again add one tablespoon of your original cabbage-indicator solution to a small, white paper cup and add drops of the food until you see the solution change color. If the food is not in liquid form, crush it or dissolve it in a small amount of water before adding it to the indicator solution. What color did the solution become, and what does this indicate about its pH?
&bull Extra: There are other vegetables and fruits that can be used to make pH indicators as well: red onion, apple skins, blueberries, grape skins and plums. Which different sources of pigment produce the best indicators?
&bull Extra: You can use an indicator solution to write secret messages. Just use full-strength lemon juice to write an invisible message on paper and let the message dry. To reveal the message, paint cabbage-indicator over the paper with a paintbrush.
Observations and results
Did the indicator solution change color when you added the lime or lemon juice, vinegar and bleach? Did the solution color indicate that the lime or lemon juice and vinegar were acidic (had a lower pH) and that the bleach was basic (with a higher pH)?
A solution with a pH between 5 and 7 is neutral, 8 or higher is a base, and 4 or lower is an acid. Lime juice, lemon juice and vinegar are acids, so they should have turned the indicator solution red or purple color. Bleach is a strong base, therefore it should have turned the indicator solution a greenish-yellow color.
How basic or acidic a solution is depends on the amount of hydrogen ions in it. A basic solution accepts hydrogen ions (or donates electron pairs as hydroxide ions) whereas an acidic solution donates hydrogen ions (or accepts electron pairs). An indicator, like anthocyanin, responds to the levels of hydrogen ions in the solution. Anthocyanin and other biological pigments absorb certain wavelengths of light and reflect others, and it is the reflected light we see that makes them appear a certain color. Depending on the levels of hydrogen ions in the solution, the indicator pigment undergoes a chemical reaction that changes its chemical structure, making it reflect a different wavelength of light and thereby change color.
Dilute the bleach solution with water before pouring it down a drain. (Remember to keep your goggles on when you do this.)
This activity brought to you in partnership with Science Buddies
Vinegar dressing and cold storage of potatoes lowers postprandial glycaemic and insulinaemic responses in healthy subjects
Objective: To investigate the effects of cold storage and vinegar addition on glycaemic and insulinaemic responses to a potato meal in healthy subjects.
Subjects and setting: A total of 13 healthy subjects volunteered for the study, and the tests were performed at Applied Nutrition and Food Chemistry, Lund University, Sweden. Experimental design and test meals:The study included four meals freshly boiled potatoes, boiled and cold stored potatoes (8 degrees C, 24 h), boiled and cold stored potatoes (8 degrees C, 24 h) with addition of vinaigrette sauce (8 g olive oil and 28 g white vinegar (6% acetic acid)) and white wheat bread as reference. All meals contained 50 g available carbohydrates and were served as a breakfast in random order after an overnight fast. Capillary blood samples were collected at time intervals during 120 min for analysis of blood glucose and serum insulin. Glycaemic (GI) and insulinaemic indices (II) were calculated from the incremental areas using white bread as reference.
Results: Cold storage of boiled potatoes increased resistant starch (RS) content significantly from 3.3 to 5.2% (starch basis). GI and II of cold potatoes added with vinegar (GI/II=96/128) were significantly reduced by 43 and 31%, respectively, compared with GI/II of freshly boiled potatoes (168/185). Furthermore, cold storage per se lowered II with 28% compared with the corresponding value for freshly boiled potatoes.
Conclusion: Cold storage of boiled potatoes generated appreciable amounts of RS. Cold storage and addition of vinegar reduced acute glycaemia and insulinaemia in healthy subjects after a potato meal. The results show that the high glycaemic and insulinaemic features commonly associated with potato meals can be reduced by use of vinegar dressing and/or by serving cold potato products.