🍎 Total acidity of fruit and vegetable products — titration with sodium hydroxide solution, result calculated as a chosen acid, PN-A-75101-04

Food chemistry PN-A-75101-04

Overview

WHAT THE STANDARD COVERS. The “Scope” field of the PKN catalogue card, in full: “Two methods are established: potentiometric and visual. The potentiometric method consists in neutralising the acids present in the test solution by potentiometric titration with sodium hydroxide solution to pH 8,1. The visual method consists in neutralising the acids present in the test solution by titration with sodium hydroxide solution in the presence of phenolphthalein or using indicator paper. The standard replaces PN-86/A-75106”. Both methods end in the same place — neutralisation of the acids with sodium hydroxide solution; they differ in how the end of the titration is detected: a pH meter and pH 8,1 or a colour change of the indicator.

STATUS (PKN cards as of 06.11.2026). The card of PN-A-75101-04:1990 (Polish version) has the header “Withdrawn and replaced by PN-EN 12147:2000 - Polish version”: publication 24-05-1990, “Withdrawal date: 02-12-2011”, 3 pages, price group B, Food, Agriculture and Forestry Sector, KT 38 Fruit and Vegetable Products, ICS 67.080.01, “Replaces: PN-A-75106:1986 - Polish version”, “Additional elements: PN-A-75101-04:1990/Az1:2002”; the card has no “Adopts” field. The amendment PN-A-75101-04:1990/Az1:2002 (Polish version) — according to its card an additional element with the header “Withdrawn”: publication 18-12-2002, “Withdrawal date: 02-12-2011”, 1 page, KT 38; the “Scope” field, in full: “The wording of point a) of clause 1 of the standard PN-90/A-75101.04 Fruit and vegetable products. Preparation of samples and methods of physicochemical testing. Determination of total acidity was changed”. The card does not say what point a) of clause 1 concerns. SUCCESSOR — THE CHAIN OF CARDS. The card of PN-EN 12147:2000 (Polish version) “Fruit and vegetable juices -- Determination of titratable acidity” has the header “Withdrawn”: publication 11-01-2000, “Withdrawal date: 09-04-2024”, 10 pages, KT 38, ICS 67.160.20, “Adopts: EN 12147:1996 [IDT]”, “Replaces: PN-A-75101-04:1990 - Polish version”; it has no “Replaced by” field. Its “Scope” field, in full: “A method is presented for determining the titratable acidity of fruit and vegetable juices by potentiometric titration of the product analysed with a standard sodium hydroxide solution. The way of converting titratable acidity to acid content, the values of the relevant factors and the permissible limits for repeatability and reproducibility are given. Detailed data on an interlaboratory test of repeatability and reproducibility using fruit juices and nectar are also presented”. The chain of cards thus ends at a withdrawn standard with no successor. What this changes for the result: the successor covers only fruit and vegetable juices and has only the potentiometric method — the visual method (phenolphthalein, indicator paper) is not in it — and according to the card it gives the factors for conversion to acid and the permissible limits for repeatability and reproducibility; for products other than juices PKN currently names no standard, so laboratories continue to cite PN-A-75101-04.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database from the production server of 02.11.2026, read on 06.11.2026). All notations of number 75101 with sheet 04 in the reference document field: 7 entries at 7 Polish laboratories (AB 079, AB 285, AB 381, AB 452, AB 583, AB 1095, AB 1334); there are no Czech laboratories with this standard in the copy. Notations: “PN-90/A-75101/04” (AB 079, AB 285, AB 1334), “PN-A-75101-04:1990” (AB 452, AB 583, AB 1095) and “PN-90/A-75101.04” (AB 381). The amendment Az1:2002 is added by 6 of the 7 laboratories — AB 583 cites the standard without it. Points of the standard are given by one laboratory: AB 381 — “pkt 2 i pkt 3” (points 2 and 3). The “Laboratories” tab recognises all these notations and shows the same 7 laboratories (the site’s search query run on the database copy on 06.11.2026). Current PCA scope documents of these 7 laboratories (read on 06.11.2026, issues from 30.10.2025 to 19.10.2026): each of the 7 entries stands in the valid issue with the same range as in the copy; these documents contain no suspension footnote.

WHAT THE LABORATORIES TEST (complete entries from the PCA documents). Total acidity of fruit and vegetable products (AB 452 — (0,11–5) %, AB 1095 — (0,20–10) %), of fruit, vegetables and their products (AB 079 — “calculated as the appropriate acid”, (0,1–2,5) % (m/m); AB 583 — “calculated as the acid used”, (0,1–6) %; AB 1334 — “Acidity”, (0,2–20,0) %), at AB 381 also of vegetable-and-meat products and of juices and nectars — “calculated as the acid applied”, (0,2–6,0) g/100 ml; g/100 g. Technique: “Titration method” (5 laboratories), “Potentiometric titration method” (AB 1334); AB 285 gives neither technique nor range: its entry is tomato concentrate — “Total acidity calculated as citric acid relative to the extract (by calculation)”. Next to this standard: the same laboratories cite other sheets of the PN-A-75101 series — volatile acidity (sheet 05: AB 285 for tomato concentrate “relative to the extract”, together with an in-house procedure, and AB 381, AB 452, AB 1095), total extract (sheet 02: AB 079, AB 381, AB 452, AB 1095) and sugars and sugar-free extract (sheet 07: AB 285, AB 381, AB 452, AB 1095); sheets 02 and 07 have separate entries in the Knowledge Base. The acidity of fruit and vegetable juices is also described by the European standard PN-EN 12147 (a separate entry in the Knowledge Base); according to the PKN card it describes only potentiometric titration and only fruit and vegetable juices, and has itself been withdrawn since 09-04-2024.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. First — the acid used for the calculation: laboratories write “appropriate acid”, “acid applied”, “acid used”, “citric acid”; conversion to different acids gives different numbers from the same titration, so a result without the name of the acid cannot be compared either with another laboratory or with a requirement. Second — the unit: AB 079 gives % (m/m), AB 381 — g/100 ml or g/100 g; a result for a juice in g/100 ml and for a purée in g/100 g are two different quantities. Third — a result “relative to the extract” (AB 285, tomato concentrate) is the quotient of two determinations: acidity is measured according to this standard, while this entry does not measure the extract — AB 285 has total extract only in its flexible scope (“Agricultural products, food”, refractometric method, reference document “Standards”); an error in the extract carries over to the quotient. On total extract — see the entry on PN-A-75101-02. Fourth — two methods under one number: the technique “Titration method” (5 laboratories) does not say whether the end of the titration was determined with a pH meter at pH 8,1 or with an indicator; only AB 1334 states the potentiometric method explicitly, and AB 381 cites “points 2 and 3” — the scopes do not show which point is which method. It is worth stating the method in the test report.

WHAT WE DO NOT GIVE. We did not have the text of the standard or of the amendment Az1:2002 — PKN makes them available for a fee. We do not give sample preparation, the mass or volume of the test portion, the concentration of the sodium hydroxide solution, the conversion factors for individual acids or precision; we do not know which point of the standard corresponds to which method, nor what point a) of clause 1, changed by Az1:2002, concerns. We do not summarise the text of PN-EN 12147 in this entry — it has a separate entry.

Method principle

According to the card of the standard: the acids present in the test solution are neutralised by titrating it with sodium hydroxide solution — in the potentiometric method to pH 8,1 measured with a pH meter, in the visual method in the presence of phenolphthalein or with indicator paper. The consumption of the solution is converted to total acidity expressed as a chosen acid (in the scopes: the acid typical of the product or the added acid). We DO NOT GIVE the working conditions — we did not have the text of the standard.

Applications

• Fruit and vegetable products (title of the standard); in accreditation scopes also fruit and vegetables, vegetable-and-meat products, juices and nectars (AB 381) and tomato concentrate (AB 285)
• Total acidity calculated as the acid typical of the product or as the added acid; at AB 285 — relative to the extract (calculated quantity)
• In accreditation scopes: 7 Polish laboratories, ranges from 0,1 to 20,0 %

Key parameters

Standard

Standard number

PN-A-75101-04:1990 (Polish version) with amendment PN-A-75101-04:1990/Az1:2002

Title (PL)

Przetwory owocowe i warzywne — Przygotowanie próbek i metody badań fizykochemicznych — Oznaczanie kwasowości ogólnej

Title (EN)

Fruit and vegetable products — Preparation of samples and methods of physicochemical testing — Determination of total acidity

Step-by-step procedure

1. Status of the document and choice of method

   PKN card: standard withdrawn 02-12-2011, replaced by PN-EN 12147:2000, which was also withdrawn on 09-04-2024, with no successor named (status of the cards as of 06.11.2026). Choice of method: potentiometric or visual.

2. Sample preparation

   We DO NOT GIVE the preparation of the sample and of the solution for titration — we did not have the text of the standard.

3. Titration

   Potentiometric method: with sodium hydroxide solution to pH 8,1; visual method: with sodium hydroxide solution in the presence of phenolphthalein or with indicator paper (from the card).

4. Result

   Total acidity with the name of the acid used for the calculation and the unit (in the scopes: %, % (m/m), g/100 ml, g/100 g) and the name of the method; for tomato concentrate relative to the extract — also the method used to determine the extract.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Sodium hydroxide solution is corrosive — gloves and safety glasses
• TECHNICAL NOTE: the result of total acidity is given with the name of the acid used for the calculation — without it the number is not comparable

Frequently asked questions